Escherichia coli mutants deficient in RNA accumulation at high temperature.

A selection technique is described which has permitted isolation of 10 mutants that continue to form protein, but are deficient in the accumulation of rRNA at 42 degrees C. DNA-RNA hybridization experiments have demonstrated that most of these mutants are specifically defective in their ability to synthesize rRNA at the restrictive temperature. The bulk of the pulse-labeled RNA formed in such mutants at 42 degrees C appears to be mRNA, with normal instability as measured in the presence of rifampicin. The remaining mutants appear to synthesize normal levels of rRNA, but that rRNA does not accumulate in a stable form. Since all of these mutants continue to form protein, and most do not accumulate significant levels of ppGpp at 42 degrees C, it appears likely that the shut-off of rRNA synthesis at 42 degrees C does not act through a lesion in the rel locus. Thus, these mutants may reveal another element(s) required to promote ribosomal RNA formation.