Determination of the Complete Amino Acid Sequence of Protein S21 from Escherichia coli Ribosomes

Abstract

Protein S21 was digested with trypsin before and after maleylation, with chymotrypsin, thermolysin a glutamyl-specific protease. The resulting peptides were isolated and their amino acid composition determined. The amino acid sequences of selected peptides were determined either by the manual subtractive Edman method or by the dansyl-Edman procedure. Additional information was obtained from the automatic Edman degradation of the whole protein in a modified Sequenator. All these results combined yielded a complete sequence determination. Protein S21 consists of 70 amino acids (Asp1, Asn2, Thr3, Ser2, Glu8, Pro3, Gly1, Ala9, Val6, Cys1, Ile1, Leu4, Tyr2, Phe3, His1, Lys9 and Arg14). It does not contain Met or Trp. The molecular weight is 8359. Clustering of basic amino acids is observed in 5 regions. A prediction for regions with .alpha.-helices and with .beta.-sheets is included.