30-S ribosomal subunit proteins of an Escherichia coli mutant in which assembly of of the small ribosomal subunit is temperature-sensitive

Escherichia coli 219ts2, a temperature‐sensitive streptomycin‐independent revertant of the streptomycin‐dependent strain E. coli 209 is defective in 30‐S ribosomal subunit assembly at 42°C. Total 30‐S ribosomal subunit proteins of this strain contain two additional components one of which (α) migrates below and the other (β) to the right of protein S7 in two‐dimensional polyacrylamide gel analyses carried out according to Kaltschmidt and Wittmann. These two components are also resolved from normal 30‐S subunit proteins by chromatography on phosphocellulose. Tryptic fingerprinting of proteins α and β identifies α as protein S7B, the form of S7 found in B strains of E. coli and β as a mutant form of protein S4 produced by deletion of about 20 amino acids from the COOH terminus of the wild‐type protein.