The MYST family of histone acetyltransferases (HATs) plays critical roles in diverse cellular processes, such as the epigenetic regulation of gene expression. Lysine autoacetylation of the MYST HATs has recently received considerable attention. Nonetheless, the mechanism and function of the autoacetylation process are not well defined. To better understand the biochemical mechanism of MYST autoacetylation and the impact of autoacetylation on the cognate histone acetylation, we carried out detailed analyses of males-absent-on-the-first (MOF), a key member of the MYST family. A number of mutant MOF proteins were produced with point mutations at several key residues near the active site of the enzyme. Autoradiography and immunoblotting data showed that mutation of these residues affects the autoacetylation activity and HAT activity of MOF by various degrees demonstrating that MOF activity is highly sensitive to the chemical changes in those residues. We produced MOF protein in the deacetylated form by using a nonspecific lysine deacetylase. Interestingly, both the autoacetylation activity and the histone acetylation activity of the deacetylated MOF were found to be very close to that of wild-type MOF, suggesting that autoacetylation of MOF only marginally modulates the enzymatic activity. Also, we found that the autoacetylation rates of MOF and deacetylated MOF were much slower than the cognate substrate acetylation. Thus, autoacetylation does not seem to contribute to the intrinsic enzymatic activity in a significant manner. These data provide new insights into the mechanism and function of MYST HAT autoacetylation.