Initiation of synthesis of N-terminal acetylated histones with methionine

The studies presented were undertaken to clarify the unsettled question whether the synthesis of histones with a N-acetylserine residue at the amino terminal end is initiated with methionine. Histones were synthesized in vitro in a rabbit reticulocyte lysate, primed with a mRNA preparation from ascites cells. Initiation of polypeptide synthesis was investigated by using N-formyl[35S]met-tRNAfMet from yeast to label the N-termini. N-Formylmethionine was incorporated into histones H1 and H4 whose N-terminal amino acid is alpha-N-acetylserine. By comparison of tryptic peptides derived from these two histones labeled either with methionine or formylmethionine and from Edman degradation it is shown that N-terminal acetylated histones are initiated with methionine, as is the case for other eukaryotic and bacterial proteins.