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

MyoD, an essential transcription factor involved in muscle cell terminal di fferentiation, is regulated by acetylation, as are a number of other transc ription factors, but the histone acetyltransferase enzyme responsible for t his acetylation is a matter of controversy. In particular, contradictory fi ndings have been reported concerning the ability of CBP/p300 to acetylate M yoD in vitro. Here we provide an explanation for this discrepancy: although full-length p300 does indeed acetylate MyoD, a fragment of p300 correspond ing to its histone acetyltransferase domain does not. In addition to clearl y demonstrating that p300 acetylates MyoD in vitro, these results underscor e the necessity of using full-length histone acetyltransferase enzymes to d raw valid conclusions from acetylation experiments.