RFXANK (RFX-associated ankyrin-containing protein, also known as RFX-B) is a regulatory subunit of the RFX heterotetrametric transcription regulatory complex that controls MHC class II gene expression. The RFX complex consists of two RFX5 molecules (the DNA-binding subunit), one RFXAP molecule, and one RFXANK molecule. RFXANK contains five ankyrin repeats that mediate protein-protein interactions, particularly with RFX5 via recognition of a PxLPxI/L motif. RFXANK does NOT bind DNA directly; DNA binding is mediated by RFX5. RFXANK is essential for RFX complex assembly and stability, and mutations cause MHC class II deficiency (bare lymphocyte syndrome type 2, complementation group B). RFXANK functions as a transcription coactivator/coregulator, NOT as a DNA-binding transcription factor.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0045944 positive regulation of transcription by RNA polymerase II | IBA GO_REF:0000033 | ACCEPT | Summary: RFXANK is part of the RFX complex that activates transcription of MHC class II genes. The IBA annotation is appropriate as this biological process annotation reflects the functional outcome of RFX complex activity. Deep research confirms RFXANK forms the trimeric RFX complex with RFX5 and RFXAP that binds the X-box within MHC II promoters [RFXANK-deep-research-falcon.md]. Reason: The RFX complex, of which RFXANK is an essential component, activates transcription of MHC class II genes. This process-level annotation is accurate and well-supported by phylogenetic inference and experimental data across mammals. Supporting Evidence: PMID:9806546 RFXANK restores MHC-II expression in cell lines from patients in group B PMID:10938133 The bare lymphocyte syndrome, a severe combined immunodeficiency due to loss of major histocompatibility complex (MHC) class II gene expression, is caused by inherited mutations in the genes encoding the heterotrimeric transcription factor RFX (RFX-B, RFX5, and RFXAP) |
| GO:0005634 nucleus | IBA GO_REF:0000033 | ACCEPT | Summary: RFXANK localizes to the nucleus as part of the RFX transcription regulatory complex. The IBA annotation for nuclear localization is well-supported. Reason: Nuclear localization is essential for RFXANK's function in transcription regulation. Multiple experimental studies confirm nuclear localization of the RFX complex. Supporting Evidence: PMID:20732328 Two RFX5 molecules and one RFXAP molecule assemble in the cytoplasm prior to nuclear localization |
| GO:0003677 DNA binding | IEA GO_REF:0000043 | REMOVE | Summary: This IEA annotation is INCORRECT. RFXANK does NOT bind DNA directly. It contains ankyrin repeats which are protein-protein interaction domains, not DNA-binding domains. The DNA-binding component of the RFX complex is RFX5, which binds the X box motif of MHC-II promoters. Deep research confirms that RFXANK functions as an adaptor/cofactor with ankyrin repeats mediating protein-protein interactions, not DNA binding [RFXANK-deep-research-falcon.md]. The UniProt keyword mapping that generated this annotation is based on the misleading "DNA-binding protein" nomenclature. Reason: RFXANK lacks any DNA-binding domain. Its ankyrin repeats mediate protein-protein interactions with RFX5 and other partners. All experimental evidence indicates that RFX5 is the DNA-binding subunit of the RFX complex, not RFXANK. Supporting Evidence: PMID:9806546 RFXANK contains a protein-protein interaction region consisting of three ankyrin repeats. Its interaction with RFX5 and RFXAP is essential for binding of the RFX complex to MHC-II promoters. PMID:22649097 the ankyrin repeat domains of ANKRA2 and its close paralog regulatory factor X-associated ankyrin-containing protein (RFXANK) recognize a PxLPxI/L motif found in diverse binding proteins, including HDAC4, HDAC5, HDAC9, megalin, and regulatory factor X, 5 (RFX5) |
| GO:0005634 nucleus | IEA GO_REF:0000120 | ACCEPT | Summary: IEA annotation for nuclear localization based on combined automated methods. This is consistent with experimental evidence showing nuclear localization. Reason: Nuclear localization is well-established for RFXANK as part of the nuclear RFX transcription regulatory complex. Supporting Evidence: PMID:10938133 the heterotrimeric transcription factor RFX (RFX-B, RFX5, and RFXAP) |
| GO:0005737 cytoplasm | IEA GO_REF:0000120 | ACCEPT | Summary: IEA annotation for cytoplasmic localization. The RFX complex assembles in the cytoplasm before nuclear translocation, so cytoplasmic localization is expected. Reason: The RFX5-RFXAP subcomplex assembles in the cytoplasm prior to nuclear localization, consistent with cytoplasmic presence of RFXANK during complex assembly. Supporting Evidence: PMID:20732328 Two RFX5 molecules and one RFXAP molecule assemble in the cytoplasm prior to nuclear localization |
| GO:0005515 protein binding | IPI PMID:10938133 Associations and interactions between bare lymphocyte syndro... | MODIFY | Summary: This IPI annotation documents physical interaction between RFX complex components. However, GO:0005515 (protein binding) is too vague and uninformative. Reason: While protein binding is demonstrated, GO:0005515 is not informative. RFXANK has specific roles as part of a transcription regulatory complex. The annotation should be converted to a more specific term reflecting its function. Proposed replacements: transcription coactivator activity Supporting Evidence: PMID:10938133 The results identified specific domains within each of the three RFX subunits that were necessary for RFX complex formation, including the ankyrin repeats of RFX-B. |
| GO:0005515 protein binding | IPI PMID:20211142 An atlas of combinatorial transcriptional regulation in mous... | KEEP AS NON CORE | Summary: IPI annotation for protein binding from a high-throughput interaction study. GO:0005515 is not informative about the nature of the interaction. Reason: This is a high-throughput study. The annotation documents physical interactions but GO:0005515 is too vague to be a core annotation. |
| GO:0005515 protein binding | IPI PMID:25752541 Ankyrin repeats of ANKRA2 recognize a PxLPxL motif on the 3M... | KEEP AS NON CORE | Summary: This study characterized the interaction between RFXANK ankyrin repeats and the PxLPxL motif in RFX7 and other proteins. While it documents specific protein-protein interactions, GO:0005515 is not informative. Reason: The study provides structural insight into RFXANK's ankyrin repeat-mediated interactions, but protein binding is not informative for a protein whose main function is mediated through protein-protein interactions as a coactivator. Supporting Evidence: PMID:25752541 Ankyrin repeats of ANKRA2 recognize a PxLPxL motif on the 3M syndrome protein CCDC8 |
| GO:0005515 protein binding | IPI PMID:31864703 Structural basis for the recognition of RFX7 by ANKRA2 and R... | KEEP AS NON CORE | Summary: IPI annotation for protein binding. GO:0005515 is not informative. Reason: Non-informative GO:0005515 annotation from interaction studies. |
| GO:0005515 protein binding | IPI PMID:33961781 Dual proteome-scale networks reveal cell-specific remodeling... | KEEP AS NON CORE | Summary: IPI annotation from proteome-scale interactome study. GO:0005515 is not informative. Reason: High-throughput interactome data. GO:0005515 is too generic. |
| GO:0005515 protein binding | IPI PMID:40205054 Multimodal cell maps as a foundation for structural and func... | KEEP AS NON CORE | Summary: IPI annotation from multimodal cell maps study. GO:0005515 is not informative. Reason: High-throughput interactome data. GO:0005515 is too generic for RFXANK's functionally important protein interactions. |
| GO:0042826 histone deacetylase binding | IEA GO_REF:0000107 | ACCEPT | Summary: This annotation is based on ortholog transfer from mouse. The interaction of RFXANK/ANKRA2 family proteins with HDACs is documented in the literature. RFXANK's ankyrin repeats recognize a PxLPxI/L motif found in HDAC4, HDAC5, and HDAC9. Reason: The related protein ANKRA2 (and by structural homology RFXANK) has been shown to bind class IIa HDACs via their PxLPxI/L motifs. This interaction is documented in PMID:22649097. Supporting Evidence: PMID:22649097 the ankyrin repeat domains of ANKRA2 and its close paralog regulatory factor X-associated ankyrin-containing protein (RFXANK) recognize a PxLPxI/L motif found in diverse binding proteins, including HDAC4, HDAC5, HDAC9 |
| GO:0005654 nucleoplasm | IDA GO_REF:0000052 | ACCEPT | Summary: IDA annotation for nucleoplasm localization based on immunofluorescence data from Human Protein Atlas. Consistent with nuclear function. Reason: Nucleoplasm localization is consistent with RFXANK's role in the RFX transcription regulatory complex. |
| GO:0005634 nucleus | IDA PMID:10938133 Associations and interactions between bare lymphocyte syndro... | ACCEPT | Summary: IDA annotation for nuclear localization from experimental study of RFX complex components. Reason: Well-supported experimental evidence for nuclear localization. Supporting Evidence: PMID:10938133 Mutagenesis of the RFX genes was performed, and the properties of the proteins were analyzed with regard to transactivation, DNA binding, and protein-protein interactions. |
| GO:0045348 positive regulation of MHC class II biosynthetic process | NAS PMID:10938133 Associations and interactions between bare lymphocyte syndro... | ACCEPT | Summary: This is the core biological function of RFXANK. The RFX complex is essential for MHC class II gene expression, and mutations in RFXANK cause MHC class II deficiency (bare lymphocyte syndrome). Reason: This is a well-established core function of RFXANK. Mutations in RFXANK abolish MHC class II expression, causing severe immunodeficiency. Supporting Evidence: PMID:9806546 RFXANK restores MHC-II expression in cell lines from patients in group B and is mutated in these patients PMID:10938133 The bare lymphocyte syndrome, a severe combined immunodeficiency due to loss of major histocompatibility complex (MHC) class II gene expression, is caused by inherited mutations in the genes encoding the heterotrimeric transcription factor RFX (RFX-B, RFX5, and RFXAP) |
| GO:0045944 positive regulation of transcription by RNA polymerase II | IDA PMID:10938133 Associations and interactions between bare lymphocyte syndro... | ACCEPT | Summary: IDA annotation for positive regulation of transcription. The RFX complex activates transcription of MHC class II genes. Reason: RFXANK is essential for RFX complex function in activating MHC class II gene transcription. Supporting Evidence: PMID:10938133 Mutagenesis of the RFX genes was performed, and the properties of the proteins were analyzed with regard to transactivation, DNA binding, and protein-protein interactions. |
| GO:0000977 RNA polymerase II transcription regulatory region sequence-specific DNA binding | IDA PMID:9806546 A gene encoding a novel RFX-associated transactivator is mut... | REMOVE | Summary: This annotation uses the "contributes_to" qualifier (in GOA), indicating RFXANK contributes to the complex's DNA binding activity. However, RFXANK does NOT bind DNA directly. The DNA-binding component of the RFX complex is RFX5, which contains the DNA-binding domain that recognizes the X box motif. RFXANK's ankyrin repeats are protein-protein interaction domains that bind RFX5, not DNA. While the "contributes_to" qualifier acknowledges that RFXANK is not the direct DNA-binding subunit, this annotation is still misleading because it implies some direct involvement in DNA binding. Reason: RFXANK does not bind DNA in any capacity. Its ankyrin repeats mediate protein-protein interactions with RFX5 and other partners. The RFX complex binds DNA through RFX5, not RFXANK. While RFXANK is required for proper complex assembly and function, this is mediated entirely through protein-protein interactions, not DNA binding. A "contributes_to" annotation for a DNA-binding term is inappropriate for a protein that has no DNA-binding activity whatsoever. Supporting Evidence: PMID:9806546 RFXANK contains a protein-protein interaction region consisting of three ankyrin repeats. Its interaction with RFX5 and RFXAP is essential for binding of the RFX complex to MHC-II promoters. PMID:22649097 the ankyrin repeat domains of ANKRA2 and its close paralog regulatory factor X-associated ankyrin-containing protein (RFXANK) recognize a PxLPxI/L motif found in diverse binding proteins |
| GO:0001228 DNA-binding transcription activator activity, RNA polymerase II-specific | IDA PMID:9806546 A gene encoding a novel RFX-associated transactivator is mut... | MODIFY | Summary: This annotation with "contributes_to" qualifier (in GOA) is INCORRECT and should be removed. GO:0001228 is defined as "A DNA-binding transcription factor activity that activates or increases transcription" - this explicitly requires DNA binding as part of the definition. RFXANK does NOT bind DNA. It contains ankyrin repeats (protein-protein interaction domains), not DNA-binding domains. The DNA-binding component of the RFX complex is RFX5, which binds the X box motif. RFXANK should be annotated as a transcription coactivator (GO:0003713), not as having DNA-binding transcription factor activity. Reason: RFXANK is a transcription coactivator/coregulator, NOT a DNA-binding transcription factor. It functions by binding to RFX5 (the DNA-binding subunit) via its ankyrin repeats recognizing the PxLPxI/L motif. The "contributes_to" qualifier does not salvage this annotation because GO:0001228 inherently requires DNA binding as part of its definition. The appropriate molecular function term for RFXANK is GO:0003713 (transcription coactivator activity), which is defined as a transcription coregulator activity that activates transcription via binding to a DNA-binding transcription factor. Proposed replacements: transcription coactivator activity Supporting Evidence: PMID:9806546 RFXANK contains a protein-protein interaction region consisting of three ankyrin repeats. Its interaction with RFX5 and RFXAP is essential for binding of the RFX complex to MHC-II promoters. PMID:22649097 the ankyrin repeat domains of ANKRA2 and its close paralog regulatory factor X-associated ankyrin-containing protein (RFXANK) recognize a PxLPxI/L motif found in diverse binding proteins, including HDAC4, HDAC5, HDAC9, megalin, and regulatory factor X, 5 (RFX5). Crystal structures of the ankyrin repeat domain of ANKRA2 in complex with its binding peptides revealed that each of the middle three ankyrin repeats of ANKRA2 recognizes a residue from the PxLPxI/L motif in a tumbler-lock binding mode PMID:10938133 DNA binding was dependent on RFX complex formation, and transactivation was dependent on a region of RFX5. |
| GO:0090575 RNA polymerase II transcription regulator complex | IPI PMID:9806546 A gene encoding a novel RFX-associated transactivator is mut... | ACCEPT | Summary: RFXANK is part of the RFX transcription regulatory complex. This cellular component annotation is appropriate. Reason: RFXANK is one of the four subunits of the heterotetrameric RFX complex that regulates MHC class II transcription. Supporting Evidence: PMID:9806546 the identification of RFXANK, the gene encoding a third subunit of RFX PMID:20732328 RFX comprises three proteins: RFX5 (two copies), RFXAP, and RFXB |
| GO:0045944 positive regulation of transcription by RNA polymerase II | IDA PMID:9806546 A gene encoding a novel RFX-associated transactivator is mut... | ACCEPT | Summary: IDA annotation for positive regulation of transcription based on the discovery paper. RFXANK restores MHC-II expression when introduced into patient cells. Deep research confirms RFXANK is essential for RFX complex function in activating MHC class II transcription [RFXANK-deep-research-falcon.md]. Reason: Well-established experimental evidence that RFXANK is required for positive regulation of MHC class II gene transcription. Supporting Evidence: PMID:9806546 RFXANK restores MHC-II expression in cell lines from patients in group B |
| GO:0003713 transcription coactivator activity | IDA PMID:9806546 A gene encoding a novel RFX-associated transactivator is mut... | NEW | Summary: RFXANK functions as a transcription coactivator as part of the RFX complex. It activates transcription of MHC class II genes by binding to the DNA-binding transcription factor RFX5 (via its ankyrin repeats), enabling the assembly and function of the RFX complex on MHC class II promoters. This is the appropriate molecular function annotation for RFXANK's role in the RFX complex. Reason: GO:0003713 (transcription coactivator activity) is defined as "A transcription coregulator activity that activates or increases the transcription of specific gene sets via binding to a DNA-binding transcription factor at a specific genomic locus, either on its own or as part of a complex." This precisely describes RFXANK's function: it activates MHC class II transcription by binding to RFX5 (the DNA-binding transcription factor) as part of the RFX complex. This annotation should replace the incorrect GO:0001228 annotation. Supporting Evidence: PMID:9806546 RFXANK contains a protein-protein interaction region consisting of three ankyrin repeats. Its interaction with RFX5 and RFXAP is essential for binding of the RFX complex to MHC-II promoters. PMID:10938133 The results identified specific domains within each of the three RFX subunits that were necessary for RFX complex formation, including the ankyrin repeats of RFX-B. DNA binding was dependent on RFX complex formation, and transactivation was dependent on a region of RFX5. PMID:22649097 the ankyrin repeat domains of ANKRA2 and its close paralog regulatory factor X-associated ankyrin-containing protein (RFXANK) recognize a PxLPxI/L motif found in diverse binding proteins, including... regulatory factor X, 5 (RFX5) |
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Download this section (compressed HTML)Q: Should RFXAP also be reclassified as a transcription coactivator rather than having DNA-binding transcription factor annotations? The same logic applies - RFXAP does not bind DNA directly.
Q: Are the GO annotations for RFX5 appropriately capturing its role as the DNA-binding subunit of the RFX complex?
Q: Should there be a specific GO term for "regulatory subunit of transcription factor complex" to better capture the roles of proteins like RFXANK and RFXAP?
Experiment: ChIP-seq comparing RFX5 binding with and without RFXANK to definitively demonstrate that RFXANK does not contribute to DNA binding specificity.
Hypothesis: RFXANK does not contribute directly to DNA binding specificity
Experiment: EMSA experiments testing purified RFXANK alone vs. RFX5 alone vs. complete RFX complex to demonstrate that only RFX5-containing complexes bind DNA.
Hypothesis: Only RFX5 provides DNA-binding activity to the RFX complex
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