This domain is the N-terminal half of the structure of histone acetyl transferase HAT1. It is often found in association with the C-terminal part of the GNAT Acetyltransf_1 (pfam00583) domain. It seems to be motifs C and D of the structure. Histone acetyltransferases (HATs) catalyze the transfer of an acetyl group from acetyl-CoA to the lysine E-amino groups on the N-terminal tails of histones. HATs are involved in transcription since histones tend to be hyper-acetylated in actively transcribed regions of chromatin, whereas in transcriptionally silent regions histones are hypo-acetylated.