We present here an in vivo view of major histocompatibility complex (MHC) class II promoter assembly, nucleosome modifications and gene expression mediated by the class II transactivator (CIITA). Acetylation and deacetylation of histones H3 and H4 at the HLA-DRA promoter were found to occur during a time-course that depended on CIITA expression and binding. Expression of a CIITA mutant, which lacked the activation domain, induced H4 but not H3 histone acetylation. This suggested that multiple histone acetyltransferase activities are associated with MHC class II expression. H4 acetylation was mapped to Lys8, which implicated several histone acetyltransferases as possible modulators of this activity.
