Binds to MYC and inhibits MYC-mediated transactivation. Also binds to MYCN and enhances MYCN-dependent transcriptional activation. Increases calpain 2-mediated proteolysis of YY1 in vitro. Component of the E2F6.com-1 complex, a repressive complex that methylates 'Lys-9' of histone H3, suggesting that it is involved in chromatin-remodeling. {ECO:0000269|PubMed:11593398, ECO:0000269|PubMed:12706874, ECO:0000269|PubMed:9016636}. This is the function of YAF2 (YY1 associated factor 2, Ensembl gene identifier ENSG00000015153).