KAL-1 (NCU03593) is a 615-residue homeodomain transcription factor of Neurospora crassa. It carries a single typical homeodomain (residues 77-136, with the WFQNRR recognition-helix motif) preceded by a disordered N-terminal region, and a C-terminal PH-like domain (Pfam PF24818, PH_TRF2_HOY1) found in a lineage of fungal homeobox proteins. The homeodomain implies sequence-specific binding to RNA polymerase II cis-regulatory DNA and action in the nucleus; no binding site, target gene or activator/repressor activity has been determined for KAL-1 itself. Its one-to-one ortholog in the rice blast fungus, TRF2 (MGG_04853), acts as a negative regulator of a polyketide (pyriculol) biosynthetic gene cluster, and the more distant Yarrowia relative HOY1, which has the same two-domain architecture, is required for the yeast-to-hypha transition. Deletion of kal-1 gives an altered colony morphology and an abnormal conidiation pattern, indicating a role in asexual development.
Existing Annotations Review
GO Term
Evidence
Action
Reason
GO:0000977 RNA polymerase II transcription regulatory region sequence-specific DNA binding
IEA GO_REF:0000117
MODIFY
Summary: ARBA-derived sequence-specific DNA-binding term. KAL-1 has a canonical homeodomain (PROSITE PS50071, residues 75-135; DNA_BIND 77-136) and sits in the PANTHER PTHR24324 SF5 subfamily, under the PAINT node that propagates the more specific cis-regulatory region binding term.
Reason: The claim is correct but less specific than the IBA-supported child term GO:0000978 (RNA polymerase II cis-regulatory region sequence-specific DNA binding), which this gene already carries. Homeodomain transcription factors bind cis-regulatory elements in promoters/enhancers, and the PTN001963821 node (which includes KAL-1) was placed with that more precise term. Refine to GO:0000978.
GO:0000978 RNA polymerase II cis-regulatory region sequence-specific DNA binding
IBA GO_REF:0000033
ACCEPT
Summary: PAINT inference from node PTN001963821, grounded in experimental DNA binding by fission yeast Phx1 and Yox1, budding yeast Pho2 and human HHEX, all PTHR24324 SF5 members. KAL-1 is in the same subfamily and retains an intact homeodomain, including the WFQNRR recognition-helix motif (residues 124-129 of the sequence).
Reason: Sequence-specific binding of cis-regulatory DNA is the ancestral activity of the homeodomain and is conserved across the experimentally characterised fungal and animal SF5 members. Nothing in the KAL-1 sequence suggests loss (homeodomain 88-93% identical to its Aspergillus and Pyricularia orthologs; full-length protein, not a fragment). The specific DNA motif is not known for KAL-1, so no more specific term is proposed.
Supporting Evidence:
file:NEUCR/kal-1/kal-1-uniprot.txt
DR PANTHER; PTHR24324:SF5; HEMATOPOIETICALLY-EXPRESSED HOMEOBOX PROTEIN HHEX; 1.
Summary: InterPro2GO mapping from the homeobox conserved-site signature (IPR017970, PROSITE PS00027), which KAL-1 matches.
Reason: A homeodomain protein with an intact DNA-recognition helix, in a subfamily whose characterised fungal members (Pho2, Yox1, Phx1) and its Pyricularia ortholog TRF2 act as transcriptional regulators, is appropriately described as an RNA polymerase II-specific DNA-binding transcription factor. The ortholog TRF2 represses its target cluster, but a single ortholog's direction of regulation is not transferred, so the activator/repressor child terms are not proposed.
Summary: Generic DNA-binding term from the homeodomain InterPro entry (IPR001356) and a UniRule.
Reason: True but uninformative. The homeodomain binds DNA sequence-specifically at cis-regulatory regions, and the gene already carries the specific descendant GO:0000978 by IBA. Refine to that term.
Summary: Nuclear location inferred from the homeodomain (PROSITE ProRule PRU00108) and UniRule.
Reason: A sequence-specific DNA-binding transcription factor must act in the nucleus. No KAL-1 localisation experiment exists, but the inference follows directly from the activity and is the expected compartment.
Supporting Evidence:
file:NEUCR/kal-1/kal-1-uniprot.txt
/evidence="ECO:0000256|PROSITE-ProRule:PRU00108"
GO:0006355 regulation of DNA-templated transcription
IEA GO_REF:0000002
MODIFY
Summary: InterPro2GO process term from the homeobox conserved-site signature.
Reason: Correct but general. The more specific descendant GO:0006357 (regulation of transcription by RNA polymerase II) is already on the gene by IBA and is consistent with the RNA polymerase II-specific transcription factor activity accepted above. Refine to GO:0006357.
GO:0006357 regulation of transcription by RNA polymerase II
IBA GO_REF:0000033
ACCEPT
Summary: PAINT inference from node PTN001963821, grounded in experimental transcription-regulation data for fungal (S. pombe Phx1 and Yox1; S. cerevisiae Pho2, Yhp1 and Yox1) and animal (HHEX orthologs, PHA-2) members of PTHR24324.
Reason: This is the process that the transcription factor activity directly executes. The function is conserved across both fungal and animal branches of the family, and KAL-1 lies inside the node with an intact homeodomain. Its Pyricularia ortholog TRF2 regulates expression of a gene cluster in vivo, consistent with this role in the KAL-1 lineage.
Supporting Evidence:
file:NEUCR/kal-1/kal-1-uniprot.txt
DR PANTHER; PTHR24324:SF5; HEMATOPOIETICALLY-EXPRESSED HOMEOBOX PROTEIN HHEX; 1.
Summary: PAINT inference from the same node, but every donor is an animal protein (mouse, rat, Xenopus and zebrafish Hhex and C. elegans PHA-2); none of the fungal members contributed to this term.
Reason: The term is very broad and the donor evidence is from animal developmental biology, which does not transfer in detail to a filamentous fungus. It is nevertheless not contradicted for KAL-1. Fungal members of the same lineage regulate developmental transitions (Yarrowia HOY1 is required for hypha formation), and the kal-1 deletion mutant has an abnormal conidiation pattern and colony morphology, so a regulatory role in fungal cell differentiation is plausible. The IBA is kept as a peripheral developmental output of the transcription factor, not a core function. A more specific fungal term such as conidiation is not proposed. The mutant phenotype shows the gene is needed for normal conidiation, but it does not show which step KAL-1 regulates or which genes it targets.
deletion prevents the yeast-hypha transition both in liquid and solid media
Core Functions
Sequence-specific DNA-binding transcription factor that binds RNA polymerase II cis-regulatory DNA through its homeodomain and regulates transcription in the nucleus. Its target genes and direction of regulation are unknown in Neurospora; its rice blast ortholog TRF2 represses a secondary-metabolite gene cluster.
Q: What DNA motif does the KAL-1 homeodomain recognise, and what are its direct target genes during conidiation? Is it, like its Pyricularia ortholog TRF2, a repressor of a secondary-metabolite gene cluster?
Q: What does the C-terminal PF24818 (PH_TRF2_HOY1) PH-like domain do? It is shared with TRF2 and HOY1 but absent from the yeast and animal family members.
Suggested Experiments
Experiment: ChIP-seq or DAP-seq of tagged KAL-1, combined with RNA-seq of the Ξkal-1 strain during conidiation, to define its binding motif, direct targets and direction of regulation.
Type: ChIP-seq / RNA-seq
External Prediction Reviews
These computational predictions are reviewed separately from the GOA annotation set used for this review. The assessments below are from this project and do not constitute official GO annotations or endorsement by GO/UniProt. They are not included in the existing annotation review above.
ProtNLM2 emitted one GO prediction for KAL-1, generic DNA binding. The homeodomain and the PTHR24324:SF5 phylogenetic transfer support it, but it is less precise than the curated RNA polymerase II cis-regulatory region sequence-specific DNA binding annotation the gene already carries.
Review rationale: KAL-1 carries a canonical homeodomain (PROSITE PS50071, Pfam PF00046; DNA_BIND 77-136 with the WFQNRR recognition-helix motif) and sits in PANTHER subfamily PTHR24324:SF5, whose PAINT node PTN001963821 transfers RNA polymerase II cis-regulatory region sequence-specific DNA binding (GO:0000978) from experimentally characterised Phx1, Yox1, Pho2 and HHEX. Generic DNA binding is therefore correct, but it is already in GOA and is an ancestor of the curated GO:0000978 annotation that the gene review accepts, so it is less precise than the existing supported term. No KAL-1 DNA-binding experiment exists; PubMed has no functional study of KAL-1 or NCU03593.