A temperature-sensitive mutant in the gene rplX for ribosomal protein L24 and its suppression by spontaneous mutations in a 23S rRNA gene of Escherichia coli.

A temperature-sensitive mutant with an altered ribosomal protein L24 was analysed. Revertant analysis showed that the temperature-sensitive growth was correlated with the altered protein. A DNA segment containing the mutant rplX gene was cloned and sequenced. The GGC codon for glycine at the amino acid position 84 of the protein was found to be altered to a GAC codon for aspartic acid. By transforming the rplX mutant with a plasmid carrying the rrnB operon and by selecting for temperature-resistant transformants we obtained two spontaneous suppressor mutants in the gene for 23S rRNA. DNA sequence analysis of the region corresponding to the 5' end of the 23S rRNA showed a C to T alteration at position 33 in both mutants and an additional A to G alteration at position 466 in one of them. The results suggest intimate interaction of protein L24 and the 5' end of 23S rRNA in vivo and support a secondary structure model of the 23S rRNA which brings these mutational points into a close contact.