Acetylation of MyoD by p300 requires more than its histone acetyltransferase domain.

MyoD, an essential transcription factor involved in muscle cell terminal differentiation, is regulated by acetylation, as are a number of other transcription factors, but the histone acetyltransferase enzyme responsible for this acetylation is a matter of controversy. In particular, contradictory findings have been reported concerning the ability of CBP/p300 to acetylate MyoD in vitro. Here we provide an explanation for this discrepancy: although full-length p300 does indeed acetylate MyoD, a fragment of p300 corresponding to its histone acetyltransferase domain does not. In addition to clearly demonstrating that p300 acetylates MyoD in vitro, these results underscore the necessity of using full-length histone acetyltransferase enzymes to draw valid conclusions from acetylation experiments.