RFXAP (Regulatory Factor X-Associated Protein) is a scaffolding subunit of the heterotrimeric RFX transcription regulatory complex that controls MHC class II gene expression. The RFX complex consists of RFX5 (two copies), RFXAP, and RFXANK/RFX-B. RFXAP does NOT bind DNA directly; rather, it assembles with RFXANK to form a scaffold that recruits RFX5. This scaffold-RFX5 interaction induces a conformational change in RFX5 that exposes its DNA-binding domain, enabling the complex to bind the X-box motif in MHC class II promoters. RFXAP mutations cause MHC class II deficiency (bare lymphocyte syndrome complementation group D), demonstrating its essential role in MHC class II gene regulation. RFXAP should be classified as a transcription coactivator, not a DNA-binding transcription factor.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005634 nucleus | IBA GO_REF:0000033 | ACCEPT | Summary: RFXAP localizes to the nucleus where it functions as part of the RFX complex. UniProt indicates nuclear localization (PMID:10938133), and the protein contains a nuclear localization signal at residues 163-178. IBA annotation is consistent with experimental evidence from multiple studies. Deep research confirms nuclear localization with NLS and acidic region essential for function (RFXAP-deep-research-falcon.md). Reason: Nuclear localization is well-established for RFXAP. The protein must be in the nucleus to participate in the RFX complex that regulates MHC class II transcription. Supported by IDA evidence (PMID:10938133) and presence of NLS motif. Supporting Evidence: 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) file:human/RFXAP/RFXAP-deep-research-falcon.md RFXAP is nuclear; an internal NLS and acidic (DE) region were described, and pathogenic variants within exon 1 spanning nucleotides 116-540 can affect the NLS/acidic domain and impair nuclear function |
| GO:0006357 regulation of transcription by RNA polymerase II | IBA GO_REF:0000033 | ACCEPT | Summary: RFXAP is an essential component of the RFX complex that regulates MHC class II gene transcription. The IBA annotation at this general level is appropriate and phylogenetically sound. Deep research confirms RFXAP is essential for MHC-II transcription via the RFX complex and CIITA recruitment (RFXAP-deep-research-falcon.md). Reason: As a component of the RFX transcription regulatory complex, RFXAP is clearly involved in regulation of transcription by RNA polymerase II. This is a core function supported by extensive literature including PMID:9118943 and PMID:9806546. The general term is appropriate for IBA evidence. Supporting Evidence: PMID:9118943 RFXAP, a novel subunit of the RFX DNA binding complex is mutated in MHC class II deficiency PMID:9806546 RFX5 and RFXAP are two subunits of RFX, a multi-protein complex that binds the X box motif of MHC-II promoters file:human/RFXAP/RFXAP-deep-research-falcon.md RFXAP is one of three core proteins (RFX5, RFXAP, RFXANK) that assemble into the RFX complex recognizing the X-box within MHC class II promoters |
| GO:0003677 DNA binding | IEA GO_REF:0000120 | REMOVE | Summary: This IEA annotation is INCORRECT. RFXAP does NOT bind DNA directly. The DNA-binding subunit of the RFX complex is RFX5, which contains the DNA-binding domain. RFXAP serves as a scaffolding protein that helps assemble the complex and induces a conformational change in RFX5 to expose its DNA-binding domain. Reason: Multiple studies demonstrate that RFXAP does not bind DNA directly. The Nature Genetics paper (PMID:9806546) clearly states that RFX5 is the DNA-binding subunit. The EMBO paper (PMID:9118943) describes RFXAP as an "associated protein" of the RFX DNA binding complex, not a DNA-binding protein itself. The UniProt KW:DNA-binding annotation that generated this IEA is erroneous and should be corrected at the source. Supporting Evidence: PMID:9806546 RFX5 and RFXAP are two subunits of RFX, a multi-protein complex that binds the X box motif of MHC-II promoters PMID:20732328 RFXAP(C) is unstructured in the absence of RFX5(N) but adopts a regular structure in the RFX5(N)(2)-RFXAP(C) complex |
| GO:0005634 nucleus | IEA GO_REF:0000120 | ACCEPT | Summary: IEA annotation for nuclear localization is correct but redundant with the IBA and IDA annotations for the same term. Reason: Nuclear localization is correct for RFXAP. The IEA provides additional automated confirmation of what is already established by experimental evidence. Supporting Evidence: PMID:10938133 inherited mutations in the genes encoding the heterotrimeric transcription factor RFX |
| GO:0005515 protein binding | IPI PMID:10938133 Associations and interactions between bare lymphocyte syndro... | MARK AS OVER ANNOTATED | Summary: Protein binding annotation based on interaction studies. This is uninformative without specifying what proteins are bound. Reason: GO guidelines discourage generic "protein binding" annotations as they provide no specific functional information. RFXAP's actual function involves specific binding to RFX5 and RFXANK to form the RFX complex. More informative annotations should specify the actual binding partners and functional context. Supporting Evidence: PMID:10938133 The results identified specific domains within each of the three RFX subunits that were necessary for RFX complex formation |
| GO:0005515 protein binding | IPI PMID:20732328 Solution structure of the heterotrimeric complex between the... | MARK AS OVER ANNOTATED | Summary: Protein binding annotation from structural study of RFX5-RFXAP interaction. Uninformative as a generic annotation. Reason: This study provides detailed structural information about the RFX5(N)2-RFXAP(C) complex. The generic "protein binding" annotation fails to capture this specificity. A more appropriate annotation would be to a term describing RFX5 binding or transcription factor 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:25752541 Ankyrin repeats of ANKRA2 recognize a PxLPxL motif on the 3M... | MARK AS OVER ANNOTATED | Summary: Protein binding from large-scale interaction study (ANKRA2 study). Generic and uninformative. The interaction partner is RFXANK (O14593) which is well-established from low-throughput studies (PMID:10938133). Reason: Generic protein binding provides no specific functional insight. This appears to be from a high-throughput study. While the RFXAP-RFXANK interaction is genuine and critical for RFX complex function, the generic GO:0005515 annotation fails to capture the functional significance. Supporting Evidence: PMID:10938133 The results identified specific domains within each of the three RFX subunits that were necessary for RFX complex formation |
| GO:0005515 protein binding | IPI PMID:26496610 A human interactome in three quantitative dimensions organiz... | MARK AS OVER ANNOTATED | Summary: Protein binding from large-scale interactome study. The interaction partner is RFX5 (P48382). This interaction is well-established from structural studies (PMID:20732328). Reason: Generic protein binding provides no specific functional insight. High-throughput interactome data. While the RFXAP-RFX5 interaction is genuine and structurally characterized, the generic annotation should be replaced with more specific functional terms. 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:28514442 Architecture of the human interactome defines protein commun... | MARK AS OVER ANNOTATED | Summary: Protein binding from human interactome architecture study. The interaction partner is RFX5 (P48382), consistent with the RFX complex structure. Reason: Generic protein binding provides no specific functional insight. High-throughput interactome data. The RFXAP-RFX5 interaction is genuine but better captured by GO:0090575 (RNA polymerase II transcription regulator complex) which specifies the functional context. Supporting Evidence: PMID:20732328 RFXAP(C) is unstructured in the absence of RFX5(N) but adopts a regular structure in the RFX5(N)(2)-RFXAP(C) complex |
| GO:0005515 protein binding | IPI PMID:33961781 Dual proteome-scale networks reveal cell-specific remodeling... | MARK AS OVER ANNOTATED | Summary: Protein binding from dual proteome interactome study. Multiple interaction partners detected: RFXANK (O14593) and RFX5 (P48382), consistent with the known RFX complex architecture. Reason: Generic protein binding provides no specific functional insight. High-throughput interactome data. The interactions with RFXANK and RFX5 are genuine and represent the core RFX complex components, but the generic annotation fails to capture functional significance. Supporting Evidence: PMID:9806546 RFX5 and RFXAP are two subunits of RFX, a multi-protein complex that binds the X box motif of MHC-II promoters |
| GO:0005515 protein binding | IPI PMID:40205054 Multimodal cell maps as a foundation for structural and func... | MARK AS OVER ANNOTATED | Summary: Protein binding from multimodal cell maps study. The interaction partner is RFXANK (O14593), consistent with the RFX complex. Reason: Generic protein binding provides no specific functional insight. High-throughput interactome data. The RFXAP-RFXANK interaction is well-established as essential for RFX complex function but should be captured by more specific annotations. Supporting Evidence: PMID:9806546 Its interaction with RFX5 and RFXAP is essential for binding of the RFX complex to MHC-II promoters |
| GO:0016607 nuclear speck | IDA GO_REF:0000052 | KEEP AS NON CORE | Summary: Nuclear speck localization from HPA immunofluorescence data. May represent a subset of the protein's localization. Reason: Nuclear speck localization is based on immunofluorescence data from the Human Protein Atlas. While this may represent genuine localization, the primary functional localization of RFXAP is at MHC class II gene promoters where it functions in the RFX complex. Nuclear speck localization may represent storage or processing rather than active function. |
| GO:0005634 nucleus | IDA PMID:10938133 Associations and interactions between bare lymphocyte syndro... | ACCEPT | Summary: Nuclear localization established by direct assay in the DeSandro et al. study of BLS factors. Reason: Direct experimental evidence for nuclear localization. Essential for RFXAP's function in the nuclear RFX transcription regulatory complex. Supporting Evidence: PMID:10938133 The bare lymphocyte syndrome, a severe combined immunodeficiency due to loss of major histocompatibility complex (MHC) class II gene expression |
| GO:0045348 positive regulation of MHC class II biosynthetic process | NAS PMID:10938133 Associations and interactions between bare lymphocyte syndro... | ACCEPT | Summary: RFXAP is essential for MHC class II gene expression. Mutations in RFXAP cause MHC class II deficiency (bare lymphocyte syndrome). This is a core biological process annotation. Deep research confirms RFXAP mutations found in BLS II patients (3/18 in Iranian cohort, PMID:37584719) with complete loss of HLA-DR expression. Reason: RFXAP is absolutely required for MHC class II expression. This is demonstrated by the disease phenotype in patients with RFXAP mutations and by complementation studies showing restoration of MHC class II expression upon RFXAP transfection. Supporting Evidence: PMID:9118943 Complementation of the 6.1.6 and DA cell lines by transfection with RFXAP fully restores expression of all endogenous MHC-II genes in vivo, demonstrating that RFXAP is a novel essential MHC-II regulatory gene PMID:10938133 loss of major histocompatibility complex (MHC) class II gene expression, is caused by inherited mutations in the genes encoding the heterotrimeric transcription factor RFX file:human/RFXAP/RFXAP-deep-research-falcon.md Disruption of any RFX subunit--including RFXAP--abolishes MHC-II expression (HLA-DR) on antigen-presenting cells and causes BLS II |
| GO:0045944 positive regulation of transcription by RNA polymerase II | IDA PMID:10938133 Associations and interactions between bare lymphocyte syndro... | ACCEPT | Summary: RFXAP positively regulates transcription of MHC class II genes. This is demonstrated by the loss of MHC class II expression when RFXAP is mutated and restoration upon complementation. Reason: Core function of RFXAP. The RFX complex activates transcription of MHC class II genes. RFXAP is essential for complex assembly and therefore for transcriptional activation. Supporting Evidence: PMID:10938133 transactivation was dependent on a region of RFX5 |
| GO:0000977 RNA polymerase II transcription regulatory region sequence-specific DNA binding | IDA PMID:9118943 RFXAP, a novel subunit of the RFX DNA binding complex is mut... | MODIFY | Summary: This annotation with 'contributes_to' qualifier attempts to capture that RFXAP is part of a DNA-binding complex but does not itself bind DNA. However, this is misleading because the term explicitly describes sequence-specific DNA binding, which RFXAP does not perform. The 'contributes_to' qualifier is typically used when a protein is part of a complex that has the function, but RFXAP's contribution is enabling RFX5's DNA binding through conformational change, not through any DNA-binding activity of its own. Reason: RFXAP does NOT bind DNA - not even as a contributor. RFX5 is the DNA-binding subunit. RFXAP contributes to DNA binding indirectly by forming a scaffold with RFXANK that induces a conformational change in RFX5 to expose its DNA-binding domain. This is a regulatory function, not a DNA-binding function. The correct annotation should be to a transcription coactivator or transcription factor complex assembly term. Proposed replacements: transcription coactivator activity Supporting Evidence: PMID:9806546 RFX5 and RFXAP are two subunits of RFX, a multi-protein complex that binds the X box motif of MHC-II promoters PMID:9806546 Its interaction with RFX5 and RFXAP is essential for binding of the RFX complex to MHC-II promoters |
| 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... | MODIFY | Summary: Same issue as the PMID:9118943 annotation. RFXAP does not bind DNA. The 'contributes_to' qualifier does not fix the fundamental problem that this term describes DNA binding, which RFXAP does not perform. Reason: RFXAP serves as a scaffolding protein that enables RFX5's DNA binding. It does not itself bind DNA or contribute to DNA binding directly. Should be annotated to transcription coactivator activity instead. 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 |
| GO:0001228 DNA-binding transcription activator activity, RNA polymerase II-specific | IDA PMID:9118943 RFXAP, a novel subunit of the RFX DNA binding complex is mut... | MODIFY | Summary: THIS IS THE CORE PROBLEMATIC ANNOTATION. GO:0001228 is "DNA-binding transcription activator activity" - by definition, this requires the protein to be a DNA-binding transcription factor. RFXAP is NOT a DNA-binding protein. Even with the 'contributes_to' qualifier, this annotation is incorrect because it causes RFXAP to appear in queries for DNA-binding transcription factors (dbTFs). RFXAP is a transcription coactivator (coTF), not a dbTF. Reason: GO:0001228 explicitly describes "DNA-binding transcription activator activity" - the GO definition states this is a "DNA-binding transcription factor activity that activates or increases transcription." RFXAP does not bind DNA. The DNA-binding subunit of the RFX complex is RFX5. RFXAP and RFXANK serve as scaffolding proteins that assemble with RFX5 and induce a conformational change that exposes RFX5's DNA-binding domain. RFXAP should be annotated to GO:0003713 (transcription coactivator activity), which correctly describes its function as a non-DNA-binding component that activates transcription through a DNA-binding transcription factor. Proposed replacements: transcription coactivator activity Supporting Evidence: PMID:9118943 RFXAP, a novel subunit of the RFX DNA binding complex is mutated in MHC class II deficiency PMID:9806546 RFX5 and RFXAP are two subunits of RFX, a multi-protein complex that binds the X box motif of MHC-II promoters PMID:20732328 Two RFX5 molecules and one RFXAP molecule assemble in the cytoplasm prior to nuclear localization |
| 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: Same fundamental problem as the PMID:9118943 annotation. RFXAP is being incorrectly annotated as a DNA-binding transcription factor when it is actually a transcription coactivator. Reason: RFXAP does not bind DNA. It is a scaffolding subunit of the RFX complex that enables the DNA-binding activity of RFX5. Should be annotated to transcription coactivator activity (GO:0003713). 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 |
| GO:0090575 RNA polymerase II transcription regulator complex | IPI PMID:9118943 RFXAP, a novel subunit of the RFX DNA binding complex is mut... | ACCEPT | Summary: RFXAP is part of the RFX transcription regulatory complex. This cellular component annotation is accurate. Reason: RFXAP is a bona fide component of the RFX transcription regulator complex, as demonstrated by co-immunoprecipitation and structural studies. This is a core annotation. Supporting Evidence: PMID:9118943 RFXAP, a novel subunit of the RFX DNA binding complex is mutated in MHC class II deficiency PMID:20732328 The mammalian immune response is mediated by a heterotetrameric transcriptional control complex, called regulatory factor X (RFX) |
| GO:0090575 RNA polymerase II transcription regulator complex | IPI PMID:9806546 A gene encoding a novel RFX-associated transactivator is mut... | ACCEPT | Summary: RFXAP is part of the RFX complex. Duplicate annotation from different publication but still valid. Reason: Confirmed component of the RFX transcription regulator complex from additional publication. Supporting Evidence: PMID:9806546 RFX5 and RFXAP are two subunits of RFX, a multi-protein complex |
| GO:0045944 positive regulation of transcription by RNA polymerase II | IMP PMID:9118943 RFXAP, a novel subunit of the RFX DNA binding complex is mut... | ACCEPT | Summary: Mutant phenotype demonstrates RFXAP is required for transcriptional activation of MHC class II genes. Reason: IMP evidence from cell lines with RFXAP mutations showing loss of MHC class II gene expression, and complementation restoring expression. Core biological process function. Supporting Evidence: PMID:9118943 Complementation of the 6.1.6 and DA cell lines by transfection with RFXAP fully restores expression of all endogenous MHC-II genes in vivo |
| 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: Direct assay evidence for positive regulation of transcription. Duplicate of other evidence codes but valid. Reason: Additional experimental support for RFXAP's role in transcriptional activation. Supporting Evidence: PMID:9806546 RFXANK restores MHC-II expression in cell lines from patients in group B and is mutated in these patients |
| GO:0003713 transcription coactivator activity | IDA PMID:9118943 RFXAP, a novel subunit of the RFX DNA binding complex is mut... | NEW | Summary: NEW ANNOTATION. RFXAP should be annotated to transcription coactivator activity (GO:0003713) instead of DNA-binding transcription activator activity (GO:0001228). RFXAP functions as a non-DNA-binding component of the RFX complex that activates transcription through its interaction with the DNA-binding transcription factor RFX5. Reason: GO:0003713 (transcription coactivator activity) correctly describes RFXAP's function. The GO definition states this is "a transcription coregulator activity that activates or increases the transcription of specific gene sets via binding to a DNA-binding transcription factor." RFXAP binds to RFX5 (the DNA-binding transcription factor) and enables transcriptional activation of MHC class II genes. This is the appropriate molecular function annotation for RFXAP. Supporting Evidence: PMID:9118943 RFXAP, a novel subunit of the RFX DNA binding complex is mutated in MHC class II deficiency PMID:10938133 transactivation was dependent on a region of RFX5 PMID:20732328 RFXAP(C) is unstructured in the absence of RFX5(N) but adopts a regular structure in the RFX5(N)(2)-RFXAP(C) complex |
Loading supporting content…
Download this section (compressed HTML)Q: Should the 'contributes_to' qualifier be used to annotate scaffolding subunits to DNA-binding terms when they enable but do not perform DNA binding? The current annotation uses 'contributes_to' for GO:0001228 and GO:0000977, but this may be misleading as RFXAP does not bind DNA at all. The 'contributes_to' qualifier is typically used when a protein is part of a complex that has the function, not when the protein enables a different subunit to perform the function.
Q: Should RFXANK also be reviewed for similar annotation issues as RFXAP? RFXANK is the other scaffolding subunit of the RFX complex and likely has similar incorrect annotations to DNA-binding terms.
Loading supporting content…
Download this section (compressed HTML)Loading supporting content…
Download this section (compressed HTML)