Suppression of an Escherichia coli secAts mutant by a gene cloned from Staphylococcus carnosus

Escherichia coli mutant MM52 (secA(ts)) was transformed with a cosmid library from Staphylococcus carnosus, and a recombinant cosmid (pBO23) allowing growth at the non-permissive temperature (42 degrees C) was isolated. pBO23 also restored the growth defects of E. coli mutants IQ85 (secY(ts)) and IT41 (lep(ts)). Nucleotide sequencing revealed that the DNA fragment responsible for the suppression effect codes for a S. carnosus protein highly homologous to the ribosomal protein L13 of E. coli. The staphylococcal L13 protein was efficiently incorporated into E. coli ribosomes. Possible explanations for the effect of this polypeptide on the growth of temperature-sensitive E. coli secretion mutants are discussed.