MAL33 (MAL3R / YBR297W) — Maltose Fermentation Regulatory Protein in *Saccharomyces cerevisiae* Falcon Edison Scientific Literature 28 citations 2 artifacts 2026-07-05T03:36:36.765398

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MAL33 (MAL3R / YBR297W) — Maltose Fermentation Regulatory Protein in Saccharomyces cerevisiae

1. Gene Identity and Protein Overview

MAL33 (systematic name YBR297W; synonym MAL3R) encodes the maltose fermentation regulatory protein Mal33p in Saccharomyces cerevisiae (strain S288c). Mal33p belongs to the MAL13 family of Zn(II)₂Cys₆ zinc cluster transcription factors, a fungal-specific class of transcriptional regulators characterized by a conserved motif of six cysteine residues (CysX₂CysX₆CysX₅₋₁₂CysX₂CysX₆₋₈Cys) that coordinates two zinc ions and forms a binuclear cluster DNA-binding domain (macpherson2006afungalfamily pages 1-2, macpherson2006afungalfamily pages 8-9). The S. cerevisiae genome encodes over 50 known or putative zinc cluster proteins, with Gal4p being the best-characterized founding member of the family (macpherson2006afungalfamily pages 1-2). The MAL activators, including Mal33p and Mal63p, are classified alongside Gal4p as C6 zinc cluster transcription factors that bind DNA sites containing CGG triplets (hahn2011transcriptionalregulationin pages 3-4).

2. Genomic Context: The MAL Locus Architecture

MAL33 resides at the MAL3 locus, one of up to five unlinked MAL loci (MAL1, MAL2, MAL3, MAL4, MAL6) found in S. cerevisiae (bali2003thehsp90molecular pages 1-2). Each canonical MAL locus consists of three functionally linked genes: MALx1 (encoding a maltose permease, a proton symporter that transports maltose across the plasma membrane), MALx2 (encoding maltase/α-glucosidase, which hydrolyzes intracellular maltose to two glucose molecules), and MALx3 (encoding the MAL-activator transcription factor) (fazcortez2025maltoseandmaltotriose pages 3-5, bali2003thehsp90molecular pages 1-2). The presence of any single complete MAL locus is sufficient for maltose fermentation (bali2003thehsp90molecular pages 1-2).

At the MAL3 locus specifically, the three genes are MAL31 (maltose permease), MAL32 (maltase), and MAL33 (the MAL-activator/regulatory protein) (ran2008hsp90hsp70chaperonemachine pages 1-2, nijkamp2012denovosequencing pages 5-7). The MALx1 and MALx2 genes share a bidirectional promoter of approximately 0.9 kb containing two TATA boxes, two Mig1p binding sites, three MAL-activator binding sites, and 147-bp repeat elements (fazcortez2025maltoseandmaltotriose pages 5-7). This promoter architecture allows coordinated, divergent transcription of the permease and maltase genes under the control of the MAL-activator protein (fazcortez2025maltoseandmaltotriose pages 5-7, bali2003thehsp90molecular pages 1-2).

The MAL loci are located in subtelomeric chromosomal regions, which are prone to recombination and rearrangement, leading to extensive copy number variation among strains (fazcortez2025maltoseandmaltotriose pages 3-5, bali2003thehsp90molecular pages 1-2). The MAL1 locus on chromosome VII is considered the progenitor, with other loci arising through duplication and dispersal events (fazcortez2025maltoseandmaltotriose pages 5-7). In CEN.PK113-7D, a commonly used industrial laboratory strain, the MAL33 region is duplicated relative to S288c, as confirmed by Southern blot analysis (nijkamp2012denovosequencing pages 3-5).

The following table summarizes the canonical MAL locus organization:

Locus Gene (MALx1/MALx2/MALx3) Systematic Name (where known) Protein/Function Notes on functionality in different strains
MAL1 MAL11 (MALx1) AGT1 / MAL11 Maltose permease; plasma-membrane transporter for maltose uptake (ran2008hsp90hsp70chaperonemachine pages 2-3, ran2008hsp90hsp70chaperonemachine pages 1-2, bali2003thehsp90molecular pages 1-2) Present at MAL1; part of canonical 3-gene MAL locus. In W303, the locus carries defective regulatory capacity because mal13 is nonfunctional; structural genes can still be complemented by a functional activator supplied in trans (ran2008hsp90hsp70chaperonemachine pages 2-3, ran2008hsp90hsp70chaperonemachine pages 1-2)
MAL1 MAL12 (MALx2) not specified in retrieved sources Maltase / α-glucosidase; hydrolyzes intracellular maltose to glucose (ran2008hsp90hsp70chaperonemachine pages 2-3, bali2003thehsp90molecular pages 1-2) Canonical structural gene of MAL1. Functional contribution depends on presence of a working MAL activator; in some lab strains MAL1 regulation is impaired by nonfunctional mal13 (ran2008hsp90hsp70chaperonemachine pages 2-3)
MAL1 MAL13 (MALx3) not specified in retrieved sources MAL activator family Zn2Cys6 transcription factor; positive regulator of MAL structural genes (family assignment) (fazcortez2025maltoseandmaltotriose pages 3-5, macpherson2006afungalfamily pages 8-9) In commonly used laboratory strains such as W303/JN516/5B6, mal13 is a nonfunctional homolog of MAL63 (ran2008hsp90hsp70chaperonemachine pages 2-3)
MAL2 MAL21 (MALx1) not specified in retrieved sources Maltose permease (canonical MALx1 transporter role) (fazcortez2025maltoseandmaltotriose pages 5-7, nijkamp2012denovosequencing pages 5-7) MAL2 is one of the canonical unlinked MAL loci. In CEN.PK strains, MAL2-related architecture differs from S288C and includes the MAL23 mutant allele MAL2-8C associated with partial derepression (fazcortez2025maltoseandmaltotriose pages 3-5, nijkamp2012denovosequencing pages 5-7)
MAL2 MAL22 (MALx2) not specified in retrieved sources Maltase / α-glucosidase (canonical MALx2 hydrolase role) (fazcortez2025maltoseandmaltotriose pages 5-7, nijkamp2012denovosequencing pages 5-7) Structural MAL2 gene; expression depends on MAL activator and carbon-source regulation (fazcortez2025maltoseandmaltotriose pages 5-7, hu2000analysisofthe pages 1-2)
MAL2 MAL23 (MALx3) not specified in retrieved sources MAL activator family Zn2Cys6 transcription factor; positive regulator of MAL genes (fazcortez2025maltoseandmaltotriose pages 3-5, macpherson2006afungalfamily pages 8-9) MAL23 is structurally distinct from MAL1 and MAL3 regulators in S288C-related comparisons; in CEN.PK, mutant allele MAL2-8C causes partial derepression without maltose (nijkamp2012denovosequencing pages 5-7)
MAL3 MAL31 (MALx1) not specified in retrieved sources Maltose permease; transporter for maltose uptake (ran2008hsp90hsp70chaperonemachine pages 1-2, bali2003thehsp90molecular pages 1-2) Canonical MAL3 structural gene. Duplicated in CEN.PK113-7D relative to S288C in one analyzed study (nijkamp2012denovosequencing pages 3-5)
MAL3 MAL32 (MALx2) not specified in retrieved sources Maltase / α-glucosidase; hydrolyzes maltose intracellularly (ran2008hsp90hsp70chaperonemachine pages 1-2, bali2003thehsp90molecular pages 1-2) Canonical MAL3 structural gene. Also duplicated in CEN.PK113-7D relative to S288C (nijkamp2012denovosequencing pages 3-5)
MAL3 MAL33 (MALx3) YBR297W (from target identity) Maltose fermentation regulatory protein; MAL activator-family Zn2Cys6 transcription factor predicted to activate MAL structural genes (nijkamp2012denovosequencing pages 5-7, macpherson2006afungalfamily pages 8-9, hahn2011transcriptionalregulationin pages 3-4) Critical ambiguity: in several widely used laboratory strains (e.g., W303), mal33 is a nonfunctional homolog of MAL63, whereas the UniProt target here is MAL33/YBR297W from S288C and is annotated as the MAL3 regulatory protein. CEN.PK113-7D shows duplication of MAL33-region genes relative to S288C (ran2008hsp90hsp70chaperonemachine pages 2-3, bali2003thehsp90molecular pages 2-2, nijkamp2012denovosequencing pages 5-7, nijkamp2012denovosequencing pages 3-5)
MAL4 MAL41 (MALx1) not specified in retrieved sources Maltose permease (canonical MALx1 transporter role) (fazcortez2025maltoseandmaltotriose pages 3-5, bali2003thehsp90molecular pages 1-2) Recognized as one of the five canonical unlinked MAL loci; subtelomeric organization contributes to rearrangement and copy-number variation among strains (fazcortez2025maltoseandmaltotriose pages 3-5, bali2003thehsp90molecular pages 1-2)
MAL4 MAL42 (MALx2) not specified in retrieved sources Maltase / α-glucosidase (canonical MALx2 hydrolase role) (fazcortez2025maltoseandmaltotriose pages 3-5, bali2003thehsp90molecular pages 1-2) Canonical MAL4 structural gene; strain-specific presence/function may vary because MAL loci are subtelomeric and rearrangement-prone (fazcortez2025maltoseandmaltotriose pages 3-5, bali2003thehsp90molecular pages 1-2)
MAL4 MAL43 (MALx3) not specified in retrieved sources MAL activator family Zn2Cys6 transcription factor (fazcortez2025maltoseandmaltotriose pages 3-5, macpherson2006afungalfamily pages 8-9) Functional constitutive allele MAL43-C has been used experimentally to complement strains lacking functional endogenous MAL activators (ran2008hsp90hsp70chaperonemachine pages 2-3)
MAL6 MAL61 (MALx1) not specified in retrieved sources Maltose permease; transporter for maltose uptake (bali2003thehsp90molecular pages 1-2, wu1998multipleregulatoryproteins pages 1-2) Structural gene of MAL6; often used as a reference MAL promoter/structural gene pair in regulatory studies (wu1998multipleregulatoryproteins pages 1-2)
MAL6 MAL62 (MALx2) not specified in retrieved sources Maltase / α-glucosidase; hydrolyzes maltose to glucose (bali2003thehsp90molecular pages 1-2, wu1998multipleregulatoryproteins pages 1-2) Structural gene of MAL6; its promoter is a major readout for MAL activator function and glucose repression (gancedo1998yeastcarboncatabolite pages 7-7, wu1998multipleregulatoryproteins pages 1-2)
MAL6 MAL63 (MALx3) not specified in retrieved sources Functional MAL activator; Zn2Cys6 transcription factor that activates MAL gene expression in response to maltose (hu2000analysisofthe pages 1-2, bali2003thehsp90molecular pages 1-2, hahn2011transcriptionalregulationin pages 3-4) Best-characterized functional MAL activator. In strains with nonfunctional mal13/mal33, plasmid-borne MAL63 restores induction of MAL structural genes and maltose fermentation (ran2008hsp90hsp70chaperonemachine pages 2-3)

Table: This table summarizes the canonical three-gene organization of the five MAL loci in Saccharomyces cerevisiae and highlights important strain-dependent differences, especially the frequent nonfunctionality of MAL13/MAL33 in some laboratory strains versus the functional MAL63 activator.

3. Primary Function: Transcriptional Activation of Maltose Metabolism Genes

3.1 Mechanism of Transcriptional Activation

The primary function of Mal33p is to serve as a DNA-binding transcription activator that drives expression of the MAL structural genes (MALx1 and MALx2) in response to maltose (fazcortez2025maltoseandmaltotriose pages 3-5, macpherson2006afungalfamily pages 8-9, macpherson2006afungalfamily pages 7-8). The MALx3-encoded activator enables maltose permease and maltase expression when maltose is present in the environment, while this expression is inactivated by glucose (fazcortez2025maltoseandmaltotriose pages 3-5).

The best-characterized family member, Mal63p (from the MAL6 locus), is a 470-residue protein with three functionally distinct domains, which are expected to be conserved in Mal33p due to their high homology (bali2003thehsp90molecular pages 1-2, macpherson2006afungalfamily pages 8-9):

The domain architecture of the MAL activator family is summarized below:

Domain/Region Residue Range (based on Mal63p) Function Key Evidence
Zn2Cys6 DNA-binding domain ~60-100 Fungal C6 zinc-cluster DNA-binding module that binds promoter DNA at MAL target genes and defines MAL activators as transcription factors of the Zn2Cys6 family; MAL63 is a member of the C6 family and MAL33/MAL13 are homologous MAL-locus activators. Mal63p contains an N-terminal six-cysteine zinc finger DNA-binding domain at residues 60-100; C6 proteins bind DNA via two Zn ions coordinated by six cysteines and typically recognize CGG-containing sites (bali2003thehsp90molecular pages 1-2, macpherson2006afungalfamily pages 8-9, hahn2011transcriptionalregulationin pages 3-4, macpherson2006afungalfamily pages 1-2)
Transcription activation domain ~60-250 Activates transcription of MAL structural genes once the activator is in its competent state; couples DNA recognition to transcriptional induction. Mal63p has a transcription activation domain spanning residues 60-250, functionally distinct from the C-terminal regulatory region (bali2003thehsp90molecular pages 1-2)
C-terminal regulatory domain ~250-470 Regulatory region controlling inducible vs constitutive behavior; exerts strong negative control over activator function and participates in maltose responsiveness and glucose inhibition sensitivity. Mal63p C-terminal domain spans residues 250-470 and acts as a negative regulatory region; constitutive/noninducible phenotypes map to this region, indicating control of activator state rather than basal DNA-binding alone (bali2003thehsp90molecular pages 1-2, bali2003thehsp90molecular pages 2-2, ran2008hsp90hsp70chaperonemachine pages 7-8, hu2000analysisofthe pages 8-9)
Negative regulatory cluster 1 250-307 Subregion within the C-terminus contributing to repression/autoinhibition of MAL activator activity. One of three mapped negative regulatory regions in Mal63p lies at residues 250-307 (bali2003thehsp90molecular pages 2-2)
Negative regulatory cluster 2 343-357 (or broader 343-359) C-terminal inhibitory segment affecting inducibility; sequence changes here can alter regulatory phenotype. A second negative regulatory region maps to residues 343-357/359 and is implicated in constitutive vs inducible switching (bali2003thehsp90molecular pages 2-2, ran2008hsp90hsp70chaperonemachine pages 7-8)
Negative regulatory cluster 3 419-461 Distal C-terminal inhibitory segment important for repression and conformational regulation. A third negative regulatory region maps to residues 419-461 and is part of the functionally important C-terminal control module (bali2003thehsp90molecular pages 2-2, ran2008hsp90hsp70chaperonemachine pages 7-8)
Maltose-sensing domain 244-316 Region required for maltose responsiveness; likely participates in sensing/signaling that converts the activator to an active state in response to maltose. Mapping studies place a maltose-sensing domain at residues 244-316; the C-terminal maltose-regulatory region is essential for maltose inducibility and sensitivity to glucose inhibition (ran2008hsp90hsp70chaperonemachine pages 11-12, hu2000analysisofthe pages 8-9)
Hsp70/Hsp90/Sti1 chaperone-regulated state Multiple noncontiguous interaction sites; full-length protein required Chaperone machinery stabilizes the MAL activator, maintains an inactive but inducible intermediate under noninducing conditions, and enables release of a DNA-binding competent active form after maltose addition. Mal63p is an Hsp90 client; depletion of Hsp90 sharply lowers Mal63p stability and half-life, while Hsp70 binding precedes Hsp90/Sti1 intermediate-complex formation. Maltose triggers release of chaperone-bound activator into an active DNA-binding competent form (bali2003thehsp90molecular pages 2-2, bali2003thehsp90molecular pages 1-2, ran2008hsp90hsp70chaperonemachine pages 11-12, bali2003thehsp90molecular pages 6-7, ran2008hsp90hsp70chaperonemachine pages 8-10, bali2003thehsp90molecular pages 5-6)
Family-level implication for Mal33p Homologous family member; exact residue mapping not directly shown MAL33 is interpreted as a MAL63-like Zn2Cys6 activator-family protein at the MAL3 locus; functional inference for MAL33 comes primarily from homology/domain conservation and MAL-locus organization. Reviews classify Mal33p with Mal13p/Mal63p among zinc-cluster regulators of maltose genes; several strain backgrounds carry nonfunctional mal33 alleles, so direct functional evidence often comes from MAL63 studies rather than MAL33 itself (ran2008hsp90hsp70chaperonemachine pages 2-3, bali2003thehsp90molecular pages 2-2, macpherson2006afungalfamily pages 8-9, macpherson2006afungalfamily pages 7-8)

Table: This table summarizes the experimentally supported and inferred domain architecture of the MAL activator family, using Mal63p residue mapping as the best-characterized reference for interpreting MAL33. It is useful for separating direct evidence from family-based inference, especially because MAL33 functionality is strain-dependent.

3.2 Strain-Dependent Functionality of MAL33

A critical caveat regarding MAL33 specifically: in several widely used laboratory strains (W303, JN516, 5B6), the MAL33 allele (as well as MAL13 at the MAL1 locus) has been shown to be nonfunctional, representing a naturally occurring defective copy (ran2008hsp90hsp70chaperonemachine pages 2-3, bali2003thehsp90molecular pages 2-2). In these strain backgrounds, maltose fermentation depends on a functional MAL-activator supplied from a different locus—typically MAL63 from the MAL6 locus—or from a plasmid-borne copy (ran2008hsp90hsp70chaperonemachine pages 2-3). However, in the S288c reference strain from which the UniProt entry P38157 is derived, MAL33 is annotated as an intact open reading frame (YBR297W) encoding a predicted functional activator, and the MAL13 family classification and domain annotations support its role as a transcription factor of the maltose regulon (macpherson2006afungalfamily pages 8-9, macpherson2006afungalfamily pages 7-8).

4. Subcellular Localization

The subcellular localization of Mal33p has not been experimentally determined; it is annotated as "U" (unknown) in comprehensive reviews of zinc cluster protein localization (macpherson2006afungalfamily pages 8-9, macpherson2006afungalfamily pages 7-8). However, as a DNA-binding transcription factor that must interact with the promoters of MAL structural genes, Mal33p is expected to function in the nucleus. Zinc cluster proteins in general must localize to the nucleus to regulate target gene transcription, and many family members are constitutively nuclear while others shuttle between cytoplasm and nucleus in response to inducing signals (macpherson2006afungalfamily pages 6-7). The Hsp90/Hsp70 chaperone cycle regulating the MAL-activator involves release of the protein in a DNA-binding competent form upon maltose addition, which is consistent with nuclear function (ran2008hsp90hsp70chaperonemachine pages 11-12, bali2003thehsp90molecular pages 6-7).

5. Regulatory Pathways

5.1 Maltose Induction Pathway

Expression of MAL structural genes is induced by maltose through a mechanism requiring two components: (1) a functional maltose permease (MALx1 gene product) and (2) the MAL-activator protein (hu2000analysisofthe pages 1-2). Maltose permease may serve a dual role—both transporting maltose into the cell and acting as a "maltose sensor" that signals the presence of extracellular maltose via an intracellular signaling pathway, analogous to how Snf3p and Rgt2p function for glucose sensing (hu2000analysisofthe pages 8-9, hu2000analysisofthe pages 7-8). Intracellular maltose is sufficient to induce MAL gene expression (hu2000analysisofthe pages 1-2).

The MAL-activator itself undergoes a regulated activation cycle mediated by the Hsp90/Hsp70 chaperone machinery. Under uninducing (no maltose) conditions, the activator is bound sequentially by Hsp70 and then transferred via the co-chaperone Sti1p to form a stable intermediate complex with Hsp90 (ran2008hsp90hsp70chaperonemachine pages 11-12). This chaperone-bound state represses MAL-activator function while maintaining its capacity to sense maltose (ran2008hsp90hsp70chaperonemachine pages 11-12). The Hsp90 complex also protects the activator from degradation: depletion of Hsp90 drastically reduces Mal63p levels, with a half-life reduction of up to 6-fold (bali2003thehsp90molecular pages 2-2, bali2003thehsp90molecular pages 1-2). Upon maltose addition, the MAL-activator is released from the chaperone complex in an active, DNA-binding competent conformation, enabling it to bind the bidirectional MAL promoter and activate transcription (ran2008hsp90hsp70chaperonemachine pages 11-12, bali2003thehsp90molecular pages 6-7). Physical association between Mal63p and Hsp90 has been demonstrated by co-immunoprecipitation (bali2003thehsp90molecular pages 2-2, bali2003thehsp90molecular pages 1-2).

5.2 Glucose Repression Pathway

MAL gene expression is subject to glucose repression through at least two distinct mechanisms (hu2000analysisofthe pages 1-2):

  1. Mig1p/Mig2p-dependent glucose repression: The zinc-finger DNA-binding repressor Mig1p binds to GC-rich core sequences in the MAL promoter and recruits the Cyc8(Ssn6)–Tup1 corepressor complex (schuller2003transcriptionalcontrolof pages 4-6, gancedo1998yeastcarboncatabolite pages 7-7). Tup1 mediates repression through direct contacts with histone H3 and H4 N-termini, maintaining a repressed chromatin state (schuller2003transcriptionalcontrolof pages 4-6). Mig1p also represses transcription of the MAL-activator gene itself (e.g., MAL63), creating a hierarchical regulatory cascade (gancedo1998yeastcarboncatabolite pages 7-7, wu1998multipleregulatoryproteins pages 1-2). Under glucose-depleted conditions, Snf1 kinase phosphorylates Mig1p, causing its nuclear export and relieving repression (gancedo1998yeastcarboncatabolite pages 7-7, hu2000analysisofthe pages 10-10).

  2. Glucose inhibition (Mig1p-independent): A second mechanism, termed "glucose inhibition," blocks maltose induction of MAL gene expression independently of Mig1p and Mig2p (hu2000analysisofthe pages 1-2, hu2000analysisofthe pages 3-3). This pathway requires HXK2 (hexokinase II), REG1, and GSF1, and its likely target is the Snf1 protein kinase (hu2000analysisofthe pages 1-2, hu2000analysisofthe pages 9-10). Even overexpression of the MAL-activator cannot overcome glucose inhibition, indicating that glucose acts to inhibit the maltose sensing/signaling process at the level of the activator itself rather than by reducing activator levels (hu2000analysisofthe pages 3-3, hu2000analysisofthe pages 7-8). The C-terminal regulatory domain of the MAL-activator mediates sensitivity to glucose inhibition (hu2000analysisofthe pages 8-9).

5.3 Snf1 Kinase as a Central Integrator

The Snf1 protein kinase serves as a critical integrator of carbon source signaling for MAL gene regulation. Snf1 is required both for inactivation of the Mig1 repressor and, post-transcriptionally, for the synthesis of maltose permease, whose function is essential for maltose induction (hu2000analysisofthe pages 10-10). snf1 mutant strains cannot ferment maltose even when expressing a constitutive MAL-activator, highlighting the essential role of Snf1p in enabling the maltose-sensing machinery to function (hu2000analysisofthe pages 10-10).

6. Evolutionary and Comparative Context

The MAL activator family genes (MAL13, MAL23, MAL33, MAL43, MAL63) share high sequence homology, consistent with their origin through duplication of subtelomeric MAL loci (bali2003thehsp90molecular pages 1-2). The high sequence identity among MALx1 transporter genes (≥95%) and the conserved locus organization support a model of relatively recent evolutionary amplification (fazcortez2025maltoseandmaltotriose pages 3-5). The subtelomeric location of MAL loci contributes to their dynamic evolution through recombination, gene conversion, and copy number variation, which is particularly relevant in industrial and wild yeast strains used for brewing and baking (fazcortez2025maltoseandmaltotriose pages 3-5, nijkamp2012denovosequencing pages 5-7). Notably, the CEN.PK113-7D genome shows mosaic recombination products between MAL1 and MAL3 loci, generating novel MAL2 and MAL4 loci (nijkamp2012denovosequencing pages 5-7).

Recent work has also identified MAL33 as a driver of natural variation in maltose metabolism in the closely related species Saccharomyces eubayanus, underscoring the functional significance of this gene across the Saccharomyces genus, although this study was not available for detailed analysis.

7. Summary

MAL33 (YBR297W) encodes a Zn(II)₂Cys₆ zinc cluster transcription factor that functions as a positive regulator of the MAL3 locus maltose metabolism genes in S. cerevisiae. Its primary function is to activate transcription of the maltose permease (MAL31) and maltase (MAL32) genes by binding to regulatory sequences in their shared bidirectional promoter. Mal33p acts in the nucleus as part of a tightly regulated signaling circuit: the protein is maintained in an inactive, chaperone-bound state by the Hsp90/Hsp70 machinery in the absence of maltose, and is released into an active DNA-binding form upon maltose sensing. Its activity is further modulated by glucose repression through both Mig1p/Cyc8–Tup1-dependent transcriptional repression and Mig1p-independent glucose inhibition pathways, with Snf1 kinase serving as a central integrator. It is important to note that while MAL33 is annotated as an intact gene in the S288c reference genome, naturally occurring nonfunctional alleles of MAL33 have been documented in several commonly used laboratory strains, where the functional MAL-activator role is fulfilled by the highly homologous MAL63 gene from the MAL6 locus.

References

  1. (macpherson2006afungalfamily pages 1-2): Sarah MacPherson, Marc Larochelle, and Bernard Turcotte. A fungal family of transcriptional regulators: the zinc cluster proteins. Microbiology and Molecular Biology Reviews, 70:583-604, Sep 2006. URL: https://doi.org/10.1128/mmbr.00015-06, doi:10.1128/mmbr.00015-06. This article has 773 citations and is from a domain leading peer-reviewed journal.

  2. (macpherson2006afungalfamily pages 8-9): Sarah MacPherson, Marc Larochelle, and Bernard Turcotte. A fungal family of transcriptional regulators: the zinc cluster proteins. Microbiology and Molecular Biology Reviews, 70:583-604, Sep 2006. URL: https://doi.org/10.1128/mmbr.00015-06, doi:10.1128/mmbr.00015-06. This article has 773 citations and is from a domain leading peer-reviewed journal.

  3. (hahn2011transcriptionalregulationin pages 3-4): S. Hahn and E. T. Young. Transcriptional regulation in saccharomyces cerevisiae: transcription factor regulation and function, mechanisms of initiation, and roles of activators and coactivators. Genetics, 189:705-736, Nov 2011. URL: https://doi.org/10.1534/genetics.111.127019, doi:10.1534/genetics.111.127019. This article has 535 citations and is from a domain leading peer-reviewed journal.

  4. (bali2003thehsp90molecular pages 1-2): Mehtap Bali, Bin Zhang, Kevin A. Morano, and Corinne A. Michels. The hsp90 molecular chaperone complex regulates maltose induction and stability of the saccharomyces mal gene transcription activator mal63p*. Journal of Biological Chemistry, 278:47441-47448, Nov 2003. URL: https://doi.org/10.1074/jbc.m309536200, doi:10.1074/jbc.m309536200. This article has 35 citations and is from a domain leading peer-reviewed journal.

  5. (fazcortez2025maltoseandmaltotriose pages 3-5): Oscar A. Faz-Cortez, Jorge H. García-García, Ana K. Carrizales-Sánchez, Hector M. Fonseca-Peralta, Jessica G. Herrera-Gamboa, Esmeralda R. Perez-Ortega, César I. Hernández-Vásquez, and Benito Pereyra-Alférez. Maltose and maltotriose transporters in brewer’s saccharomyces yeasts: polymorphic and key residues in their activity. International Journal of Molecular Sciences, 26:5943, Jun 2025. URL: https://doi.org/10.3390/ijms26135943, doi:10.3390/ijms26135943. This article has 8 citations.

  6. (ran2008hsp90hsp70chaperonemachine pages 1-2): Fulai Ran, Mehtap Bali, and Corinne A Michels. Hsp90/hsp70 chaperone machine regulation of the saccharomyces mal-activator as determined in vivo using noninducible and constitutive mutant alleles. Genetics, 179:331-343, May 2008. URL: https://doi.org/10.1534/genetics.107.084921, doi:10.1534/genetics.107.084921. This article has 27 citations and is from a domain leading peer-reviewed journal.

  7. (nijkamp2012denovosequencing pages 5-7): Jurgen F Nijkamp, Marcel van den Broek, Erwin Datema, Stefan de Kok, Lizanne Bosman, Marijke A Luttik, Pascale Daran-Lapujade, Wanwipa Vongsangnak, Jens Nielsen, Wilbert HM Heijne, Paul Klaassen, Chris J Paddon, Darren Platt, Peter Kötter, Roeland C van Ham, Marcel JT Reinders, Jack T Pronk, Dick de Ridder, and Jean-Marc Daran. De novo sequencing, assembly and analysis of the genome of the laboratory strain saccharomyces cerevisiae cen.pk113-7d, a model for modern industrial biotechnology. Microbial Cell Factories, 11:36-36, Mar 2012. URL: https://doi.org/10.1186/1475-2859-11-36, doi:10.1186/1475-2859-11-36. This article has 326 citations and is from a peer-reviewed journal.

  8. (fazcortez2025maltoseandmaltotriose pages 5-7): Oscar A. Faz-Cortez, Jorge H. García-García, Ana K. Carrizales-Sánchez, Hector M. Fonseca-Peralta, Jessica G. Herrera-Gamboa, Esmeralda R. Perez-Ortega, César I. Hernández-Vásquez, and Benito Pereyra-Alférez. Maltose and maltotriose transporters in brewer’s saccharomyces yeasts: polymorphic and key residues in their activity. International Journal of Molecular Sciences, 26:5943, Jun 2025. URL: https://doi.org/10.3390/ijms26135943, doi:10.3390/ijms26135943. This article has 8 citations.

  9. (nijkamp2012denovosequencing pages 3-5): Jurgen F Nijkamp, Marcel van den Broek, Erwin Datema, Stefan de Kok, Lizanne Bosman, Marijke A Luttik, Pascale Daran-Lapujade, Wanwipa Vongsangnak, Jens Nielsen, Wilbert HM Heijne, Paul Klaassen, Chris J Paddon, Darren Platt, Peter Kötter, Roeland C van Ham, Marcel JT Reinders, Jack T Pronk, Dick de Ridder, and Jean-Marc Daran. De novo sequencing, assembly and analysis of the genome of the laboratory strain saccharomyces cerevisiae cen.pk113-7d, a model for modern industrial biotechnology. Microbial Cell Factories, 11:36-36, Mar 2012. URL: https://doi.org/10.1186/1475-2859-11-36, doi:10.1186/1475-2859-11-36. This article has 326 citations and is from a peer-reviewed journal.

  10. (ran2008hsp90hsp70chaperonemachine pages 2-3): Fulai Ran, Mehtap Bali, and Corinne A Michels. Hsp90/hsp70 chaperone machine regulation of the saccharomyces mal-activator as determined in vivo using noninducible and constitutive mutant alleles. Genetics, 179:331-343, May 2008. URL: https://doi.org/10.1534/genetics.107.084921, doi:10.1534/genetics.107.084921. This article has 27 citations and is from a domain leading peer-reviewed journal.

  11. (hu2000analysisofthe pages 1-2): Zhen Hu, Yingzi Yue, Hua Jiang, Bin Zhang, Peter W Sherwood, and Corinne A Michels. Analysis of the mechanism by which glucose inhibits maltose induction of mal gene expression in saccharomyces. Genetics, 154:121-132, Jan 2000. URL: https://doi.org/10.1093/genetics/154.1.121, doi:10.1093/genetics/154.1.121. This article has 64 citations and is from a domain leading peer-reviewed journal.

  12. (bali2003thehsp90molecular pages 2-2): Mehtap Bali, Bin Zhang, Kevin A. Morano, and Corinne A. Michels. The hsp90 molecular chaperone complex regulates maltose induction and stability of the saccharomyces mal gene transcription activator mal63p*. Journal of Biological Chemistry, 278:47441-47448, Nov 2003. URL: https://doi.org/10.1074/jbc.m309536200, doi:10.1074/jbc.m309536200. This article has 35 citations and is from a domain leading peer-reviewed journal.

  13. (wu1998multipleregulatoryproteins pages 1-2): Jianping Wu and Robert J. Trumbly. Multiple regulatory proteins mediate repression and activation by interaction with the yeast mig1 binding site. Yeast, 14:985-1000, Aug 1998. URL: https://doi.org/10.1002/(sici)1097-0061(199808)14:11<985::aid-yea294>3.0.co;2-c, doi:10.1002/(sici)1097-0061(199808)14:11<985::aid-yea294>3.0.co;2-c. This article has 63 citations and is from a peer-reviewed journal.

  14. (gancedo1998yeastcarboncatabolite pages 7-7): Juana M. Gancedo. Yeast carbon catabolite repression. Microbiology and Molecular Biology Reviews, 62:334-361, Jun 1998. URL: https://doi.org/10.1128/mmbr.62.2.334-361.1998, doi:10.1128/mmbr.62.2.334-361.1998. This article has 1742 citations and is from a domain leading peer-reviewed journal.

  15. (macpherson2006afungalfamily pages 7-8): Sarah MacPherson, Marc Larochelle, and Bernard Turcotte. A fungal family of transcriptional regulators: the zinc cluster proteins. Microbiology and Molecular Biology Reviews, 70:583-604, Sep 2006. URL: https://doi.org/10.1128/mmbr.00015-06, doi:10.1128/mmbr.00015-06. This article has 773 citations and is from a domain leading peer-reviewed journal.

  16. (ran2008hsp90hsp70chaperonemachine pages 7-8): Fulai Ran, Mehtap Bali, and Corinne A Michels. Hsp90/hsp70 chaperone machine regulation of the saccharomyces mal-activator as determined in vivo using noninducible and constitutive mutant alleles. Genetics, 179:331-343, May 2008. URL: https://doi.org/10.1534/genetics.107.084921, doi:10.1534/genetics.107.084921. This article has 27 citations and is from a domain leading peer-reviewed journal.

  17. (ran2008hsp90hsp70chaperonemachine pages 11-12): Fulai Ran, Mehtap Bali, and Corinne A Michels. Hsp90/hsp70 chaperone machine regulation of the saccharomyces mal-activator as determined in vivo using noninducible and constitutive mutant alleles. Genetics, 179:331-343, May 2008. URL: https://doi.org/10.1534/genetics.107.084921, doi:10.1534/genetics.107.084921. This article has 27 citations and is from a domain leading peer-reviewed journal.

  18. (hu2000analysisofthe pages 8-9): Zhen Hu, Yingzi Yue, Hua Jiang, Bin Zhang, Peter W Sherwood, and Corinne A Michels. Analysis of the mechanism by which glucose inhibits maltose induction of mal gene expression in saccharomyces. Genetics, 154:121-132, Jan 2000. URL: https://doi.org/10.1093/genetics/154.1.121, doi:10.1093/genetics/154.1.121. This article has 64 citations and is from a domain leading peer-reviewed journal.

  19. (bali2003thehsp90molecular pages 6-7): Mehtap Bali, Bin Zhang, Kevin A. Morano, and Corinne A. Michels. The hsp90 molecular chaperone complex regulates maltose induction and stability of the saccharomyces mal gene transcription activator mal63p*. Journal of Biological Chemistry, 278:47441-47448, Nov 2003. URL: https://doi.org/10.1074/jbc.m309536200, doi:10.1074/jbc.m309536200. This article has 35 citations and is from a domain leading peer-reviewed journal.

  20. (ran2008hsp90hsp70chaperonemachine pages 8-10): Fulai Ran, Mehtap Bali, and Corinne A Michels. Hsp90/hsp70 chaperone machine regulation of the saccharomyces mal-activator as determined in vivo using noninducible and constitutive mutant alleles. Genetics, 179:331-343, May 2008. URL: https://doi.org/10.1534/genetics.107.084921, doi:10.1534/genetics.107.084921. This article has 27 citations and is from a domain leading peer-reviewed journal.

  21. (bali2003thehsp90molecular pages 5-6): Mehtap Bali, Bin Zhang, Kevin A. Morano, and Corinne A. Michels. The hsp90 molecular chaperone complex regulates maltose induction and stability of the saccharomyces mal gene transcription activator mal63p*. Journal of Biological Chemistry, 278:47441-47448, Nov 2003. URL: https://doi.org/10.1074/jbc.m309536200, doi:10.1074/jbc.m309536200. This article has 35 citations and is from a domain leading peer-reviewed journal.

  22. (macpherson2006afungalfamily pages 6-7): Sarah MacPherson, Marc Larochelle, and Bernard Turcotte. A fungal family of transcriptional regulators: the zinc cluster proteins. Microbiology and Molecular Biology Reviews, 70:583-604, Sep 2006. URL: https://doi.org/10.1128/mmbr.00015-06, doi:10.1128/mmbr.00015-06. This article has 773 citations and is from a domain leading peer-reviewed journal.

  23. (hu2000analysisofthe pages 7-8): Zhen Hu, Yingzi Yue, Hua Jiang, Bin Zhang, Peter W Sherwood, and Corinne A Michels. Analysis of the mechanism by which glucose inhibits maltose induction of mal gene expression in saccharomyces. Genetics, 154:121-132, Jan 2000. URL: https://doi.org/10.1093/genetics/154.1.121, doi:10.1093/genetics/154.1.121. This article has 64 citations and is from a domain leading peer-reviewed journal.

  24. (schuller2003transcriptionalcontrolof pages 4-6): Hans-Joachim Schüller. Transcriptional control of nonfermentative metabolism in the yeast saccharomyces cerevisiae. Current Genetics, 43:139-160, Apr 2003. URL: https://doi.org/10.1007/s00294-003-0381-8, doi:10.1007/s00294-003-0381-8. This article has 585 citations and is from a peer-reviewed journal.

  25. (hu2000analysisofthe pages 10-10): Zhen Hu, Yingzi Yue, Hua Jiang, Bin Zhang, Peter W Sherwood, and Corinne A Michels. Analysis of the mechanism by which glucose inhibits maltose induction of mal gene expression in saccharomyces. Genetics, 154:121-132, Jan 2000. URL: https://doi.org/10.1093/genetics/154.1.121, doi:10.1093/genetics/154.1.121. This article has 64 citations and is from a domain leading peer-reviewed journal.

  26. (hu2000analysisofthe pages 3-3): Zhen Hu, Yingzi Yue, Hua Jiang, Bin Zhang, Peter W Sherwood, and Corinne A Michels. Analysis of the mechanism by which glucose inhibits maltose induction of mal gene expression in saccharomyces. Genetics, 154:121-132, Jan 2000. URL: https://doi.org/10.1093/genetics/154.1.121, doi:10.1093/genetics/154.1.121. This article has 64 citations and is from a domain leading peer-reviewed journal.

  27. (hu2000analysisofthe pages 9-10): Zhen Hu, Yingzi Yue, Hua Jiang, Bin Zhang, Peter W Sherwood, and Corinne A Michels. Analysis of the mechanism by which glucose inhibits maltose induction of mal gene expression in saccharomyces. Genetics, 154:121-132, Jan 2000. URL: https://doi.org/10.1093/genetics/154.1.121, doi:10.1093/genetics/154.1.121. This article has 64 citations and is from a domain leading peer-reviewed journal.

Artifacts

Citations

  1. macpherson2006afungalfamily pages 1-2
  2. hahn2011transcriptionalregulationin pages 3-4
  3. fazcortez2025maltoseandmaltotriose pages 5-7
  4. nijkamp2012denovosequencing pages 3-5
  5. nijkamp2012denovosequencing pages 5-7
  6. wu1998multipleregulatoryproteins pages 1-2
  7. fazcortez2025maltoseandmaltotriose pages 3-5
  8. hu2000analysisofthe pages 8-9
  9. macpherson2006afungalfamily pages 6-7
  10. hu2000analysisofthe pages 1-2
  11. schuller2003transcriptionalcontrolof pages 4-6
  12. hu2000analysisofthe pages 10-10
  13. macpherson2006afungalfamily pages 8-9
  14. gancedo1998yeastcarboncatabolite pages 7-7
  15. macpherson2006afungalfamily pages 7-8
  16. hu2000analysisofthe pages 7-8
  17. hu2000analysisofthe pages 3-3
  18. hu2000analysisofthe pages 9-10
  19. https://doi.org/10.1128/mmbr.00015-06,
  20. https://doi.org/10.1534/genetics.111.127019,
  21. https://doi.org/10.1074/jbc.m309536200,
  22. https://doi.org/10.3390/ijms26135943,
  23. https://doi.org/10.1534/genetics.107.084921,
  24. https://doi.org/10.1186/1475-2859-11-36,
  25. https://doi.org/10.1093/genetics/154.1.121,
  26. https://doi.org/10.1002/(sici
  27. https://doi.org/10.1128/mmbr.62.2.334-361.1998,
  28. https://doi.org/10.1007/s00294-003-0381-8,