The MSL complex has histone acetyltransferase (HAT) activity with a high specificity for histone H4 lysine-17 (H4K16) (Smith et al. 2000, 2005, Conrad et al. 2012). The subunit responsible for this activity is KAT8 (Males Absent on the First, MOF) a member of the MYST (named for yeast and human members MOZ, YBF2, SAS2, and Tip60) HAT family. In Drosophilla, the MSL complex associates at hundreds of sites along the X chromosome in somatic cells, resulting in the hyperacetylation of H4K16 (Lavender et al. 1994, Smith et al. 2000). In humans MSL is responsible for the majority of H4 acetylation at lysine-17 in the cell. KAT8 is a component of other complexes (Smith et al. 2005, Mendjan et al. 2006, Cai et al. 2010).