Polycomb group (PcG) protein. While PcG proteins are generally required to maintain the transcriptionally repressive state of homeotic genes throughout development, this protein is specifically required during the first 6 hours of embryogenesis to establish the repressed state. Component of the Esc/E(z) complex, which methylates 'Lys-9' and 'Lys-27' residues of histone H3, leading to transcriptional repression of the affected target gene. The Esc/E(z) complex is necessary but not sufficient for the repression of homeotic target genes, suggesting that the recruitment of the distinct PRC1 complex is also required.

(UniProt, Q24338)

Distal portions of second and third legs weakly transformed into first leg and wing blade into haltere; transformation partial and variable in hypomorphic allele, esc1. Sex combs may be present on all six legs of male; at least one extra sex comb present in majority of males. Expression affected by culture conditions. When expressivity high, extra transverse bristle rows appear between sixth and eighth longitudinal rows of bristles, mainly on distal portion of basitarsus and tibia of second and third legs in both sexes; accompanied by shortening of affected leg segments. Sex comb development autonomous in mosaics produced by somatic crossing over [Tokunaga and Stern, 1965, Dev. Biol. 11: 50-81 (fig.)]. For interactions with Pc and Scx see Hannah-Alava [1958, Genetics 43: 878-905 (fig.)]. Leg effects autonomous in homozygous clones of hypomorphic or amorphic alleles. Studies with amorphic alleles demonstrate that esc offspring of esc/+ mothers express the leg transformation, but esc zygotes produced by esc mothers die as newly hatched larvae that exhibit drastic homeotic transformations. All abdominal and thoracic and some head segments are transformed into eighth abdominal segments. The effects of the maternal insufficiency partially overcome by the presence in the zygote of a paternally derived esc+ allele, more so by two paternally derived esc+ alleles. Larvae with one paternal esc+ range between normal and transformed phenotype; those with two frequently develop into adults, more than half of which show patchy transformations in abdominal and thoracic segments to more posterior segments. Temperature-shift experiments with the temperature-sensitive allele, esc17 (i.e., on the esc/esc progeny of esc17/esc mothers when crossed to esc fathers) indicate that esc+ product is required only around the time of gastrulation, as that is the only temperature-sensitive period (Struhl and Brower, 1982, Cell 31: 285-92). In the presence of extreme BXC deficiencies (including abdA-, AbdB-, and abdA- AbdB-) which transform the eighth abdominal segment to more anterior segments, esc+ product insufficiency in the zygote causes all segments to develop as the eighth abdominal segment would develop under the influence of the BXC genotype in the presence of esc+ product (Struhl, 1981; Struhl and White, 1985, Cell 43: 507-19). In the esc- embryo produced by esc2/esc10 parents, Ubx transcription is normal early in development, but following gastrulation transcripts appear in ectodermal and mesodermal derivatives of all fourteen parasegments rather than being restricted to parasegments 6-12 as in wild-type (Struhl and Akam, 1985, EMBO J. 4: 3259-64). esc- embryos display reduced levels of Antp protein to levels below those of wild-type in all segments of the nervous system (Carroll, Laymon, McCutcheon, Riley, and Scott, 1986, Cell 47: 113-22).