The coat protein of the RNA bacteriophage MS2

Abstract

The amino acid composition of the coat protein of the MS2 phage seems to be identical to that of M12. The f2 phage differs from these by one methionine to leucine exchange and the R17, seemingly, by a glutamic acid or amide to lysine exchange. Alanine was found to be the N-terminal amino acid, and tyrosine preceded by isoleucine the C-terminal amino acids of the MS2 protein. All 11 unique tryptic fragments of the MS-2 protein have been separated and analyzed. By amino ethylation, followed by tryptic digestion, it was possible to locate the two cysteine residues and by cyanogen bromide cleavage the two methionine residues. The latter technique has been of particular advantage in lessening the interaction of the core peptides obtained upon tryptic digestion, and facilitating the isolation of the biggest peptide. Cyanogen bromide cleavage, in conjunction with the isolation of peptides resulting from subsequent thermolysin digestion, has also made it possible to align all tryptic peptides in a unique sequence.