A TEMPERATURE-SENSITIVE MUTANT OF ESCHERICHIA-COLI WITH AN ALTERATIONIN RIBOSOMAL-PROTEIN L22

A temperature-sensitive, protein synthesis-defective mutant of Escheri chia coil exhibiting an altered ribosomal protein L22 has been investi gated. The temperature-sensitive mutation was mapped to the rplV gene for protein L22. The genes from the wild type and mutant strains were amplified by the polymerase chain reaction and the products were seque nced. A cytosine to thymine transition at position 22 of the coding se quence was found in the mutant DNA, predicting an arginine to cysteine alteration in the protein. A single cysteine residue was found in the isolated mutant protein. This amino acid change accounts for the alte red mobility of the mutant protein in two-dimensional gels and during reversed-phase HPLC. The temperature-sensitive phenotype was fully com plemented by a plasmid carrying the wild type L22 gene. Ribosomes from the complemented cells showed only wild type protein L22 by two dimen sional gel analysis and were as heat-resistant as control ribosomes in a translation assay. The point mutation in the L22 gene is uniquely r esponsible for the temperature-sensitivity of this strain.