The Msl proteins are essential for elevating transcription of the single X chromosome in the male (X chromosome dosage compensation). Msl-1 is a pioneer protein. 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. In complex with msl-2, promotes ubiquitination of histone H2B. Component of the male-specific lethal (MSL) histone acetyltransferase complex at least composed of mof, msl-1, msl-2 and msl-3 (PubMed:16543150). Interacts with tamo via the nuclear localization signal (PubMed:12653959). Msl-1 is associated with hundreds of discrete sites along the length of the X chromosome in males and not in females, and is also associated with 10-20 autosomal sites in males. Belongs to the msl-1 family.