The MSL proteins are essential for elevating transcription of the single X chromosome in the male (X chromosome dosage compensation). Mle, msl-1 and msl-3 are colocalized on the X chromosome. Each of the MSL proteins requires all the other MSLs for wild-type X-chromosome binding.

(UniProt, P50536)

Homozygous males exhibit delayed development; survive as larvae for ten days. Ten-day-old male larvae have small undeveloped imaginal discs, which, however, when transplanted into wild type larvae are capable of undergoing nearly complete (wing, leg) or partial (eye-antenna) differentiation; few homozygous mle gynandromorphs survive; XO patches small, with small bristles, and mostly confined to abdomen [Uenoyama, Uchida, Fukunaga, and Oishi, 1982, Genetics 102: 223-31(fig.)]. No interaction with mle. Females transformed into phenotypic males (tra, tra2) or intersexes (dsx) unaffected by mle3, i.e. mle3 acts only upon single-X-bearing flies. Females heterozygous for SxlF1 and homozygous (and to a lesser extent heterozygous) for mle3 show signs of intersexual development; effect less severe when mothers homozygous for mle3 [Uenoyama, Fukunaga, and Oishi, 1982, Genetics 102: 233-43 (fig.)]. Staining of polytene X chromosome of mle3 males similar to that of mle males (Lucchesi, Skripsky, and Tax, 1982, Genetics 100: s42; Okuno, Satou, and Oishi, 1984, Jpn. J. Genet. 59: 237-47).