Essential protein required for proper condensation of mitotic chromosomes and progression through mitosis (PubMed:9463384). Binds to specific polytene chromosome sites, many of which are shared with the posterior sex combs (Psc) protein (PubMed:9463384). Involved in maintaining Abd-B repression outside its normal expression domain (PubMed:18667003, PubMed:18286205). Homodimer (PubMed:12771214). Interacts with esc, Trl, E(z), scm and ph-p in vitro (PubMed:12771214). Found in vivo in an esc-containing complex, which may be the Esc/E(z) complex (PubMed:12771214). Also found in vivo in a Pc-containing complex that may be the PRC1 complex, but does not interact with Pc directly (PubMed:12771214). Interacts with cyclin CycG (PubMed:18286205). Expressed during oogenesis, embryonic and larval stages.