Acts as component of the STAGA transcription coactivator-HAT complex. Mediates the interaction of STAGA complex with the CRX and is involved in CRX-dependent gene activation. Necessary for microtubule cytoskeleton stabilization. Component of the STAGA transcription coactivator-HAT complex, at least composed of SUPT3H, GCN5L2, TAF5L, TAF6L, SUPT7L, TADA3L, TAD1L, TAF10, TAF12, TRRAP, TAF9 and ATXN7. The STAGA core complex is associated with a subcomplex required for histone deubiquitination composed of ATXN7L3, ENY2 and USP22. Interacts with SORBS1, PSMC1 and CRX. Interacts with TRRAP, GCN5L2 and TAF10. Interacts with alpha tubulin. In addition to a diffuse distribution throughout the nucleus, it is associated with the nuclear matrix and the nucleolus. It is able to shuttle between the nucleus and cytoplasm. Isoform a and isoform b are expressed in CNS, but isoform a is expressed predominantly in the peripherical tissues. Isoform b is also highly expressed in the frontal lobe, skeletal muscle and spinal cord and is expressed at a lower level in the lung, lymphoblast and intestine. Proteolytically cleaved. The cleavage may be involved in SCA7 degeneration: the isoform fragments may exert distinct toxic influences that could contribute to selective neurodegeneration. Sumoylation decreases the aggregation propensity and cellular toxicity of forms with an expanded poly-Gln region but has no effect on subcellular location or interaction with components of the STAGA complex. The poly-Gln region of ATXN7 is highly polymorphic (4 to 18 repeats) in the normal population and is expanded to about 38-130 repeats in SCA7 patients. Intermediate alleles with 28 to 35 repeats are prone to further expansion. The disease is caused by variants affecting the gene represented in this entry. Belongs to the ataxin-7 family.