The Amino Acid Sequence of an Extracellular Nuclease of Staphylococcus aureus

I. LINEAR ORDER OF THE FRAGMENTS PRODUCED BY CLEAVAGE WITH CYANOGEN BROMIDE

From the ¹ From the Laboratory of Chemical Biology, National Institute of Arthritis and Metabolic Diseases, National Institutes of Health, Bethesda, Maryland 20014

An extracellular nuclease of Staphylococcus aureus, strain V8, was purified to a state of sufficient homogeneity for the study of its covalent structure. The purified enzyme exhibits both ribonuclease and deoxyribonuclease activities. The protein contains alanine and glutamine as the amino- and carboxyl-terminal residues, respectively. Neither cysteine nor cystine is present. Cyanogen bromide digestion of the nuclease yielded five fragments, designated A, B, C, D, and E. These fragments have been purified and analyzed for amino acid composition. Fragments A, B, and C contain amino-terminal alanine, tyrosine, and threonine, respectively. Both D and E have valine as the amino-terminal residue. Homoserine was found in A, B, C, and D, whereas the carboxyl-terminal residue of E was glutamine. Tryptic peptides of each of fragments A, C, D, and E have been separated and analyzed for amino acid composition and amino-terminal residues. The tryptic peptides of the nuclease containing methionine have also been isolated and similarly examined. By a consideration of these results and the total amino acid composition of the nuclease, together with examination of tryptic peptide maps, the minimum molecular weight of the nuclease has been calculated to be approximately 17,000, and the cyanogen bromide fragments have been assigned the order A-B-C-D-E.

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