Analysis of rpsD mutations in Escherichia coli. I. Comparison of mutants with various alterations in ribosomal protein S4.

Streptomycin-independent revertants were selected from streptomycin-dependent mutants. Twenty-five out of 150 such revertants were temperature sensitive. Ribosomal proteins from 18 temperature-sensitive and 10 temperature-insensitive revertants were analysed by SDS-polyacrylamide gel electrophoresis. Seventeen of the former but none of the latter category showed an alteration of protein S4. The mutated rpsD allele of 6 temperature-sensitive revertants was transduced into a rpsL+ strain. In all cases an increased suppressibility of T4 amber phages was observed. Such suppressibility was not observed in the original rpsD, rpsL strains. All 18 temperature-sensitive mutants were disturbed in the processing of 17s to 16s RNA at non-permissive temperature and the accumulated 17s RNA was degraded. Temperature-insensitive rpsD revertants could be isolated, which had gained a second alteration in S4. Such revertants, which had lost the temperature-sensitive property, were also unable to suppress growth of T4 amber phages. It is concluded that temperature-sensitive growth, inability to process 17s RNA and to assemble 30S ribosomes at non-permissive temperature as well as increased translational ambiguity are highly correlated properties in rpsD mutants.