In vivo NH2-terminal acetylation of Sindbis virus proteins

The in vivo incorporation of exogenous radioactive acetate into two proteins of Sindbis virus, the capsid protein and PE2, is described. Under appropriate labeling conditions, 40-50% of the label in the capsid protein is found in an N-acetyl group which constitutes the NH2-terminal modification of this blocked protein. The incorporated radiolabeled acetate was useful in the purification and analysis of peptides derived from the NH2-terminus of the capsid protein, and from these peptides the NH2-terminal sequence of the protein was determined to be N-acetyl-Met-Asx-, with the asx group most likely asparagine. The analysis of a peptide derived from the NH2-terminus of PE2 and containing 45% of the acetate-derived label in this protein leads us to conclude that at least a significant fraction of PE2 is also blocked by N-acetylation.