Guanine nucleotide metabolism in a mutant strain of Escherichia coli with a temperature sensitive lesion in rRNA synthesis.

We have described a mutant of Escherichia coli (designated 2S142) which shows specific inhibition of rRNA synthesis at 42 degrees C. ppGpp levels increase at the restrictive temperature, as expected. However, when the cells are returned to 30 degrees C, rRNA synthesis resumes before ppGpp levels have returned to normal. Furthermore, when ppGpp levels are decreased by the addition of tetracycline or choramphenicol, rRNA synthesis does not resume at 42 degrees C. Also, a derivative of 2S142 with a temperature-sensitive G factor (which cannot synthesize either protein or ppGpp at 42 degrees C) shows identical kinetics of rRNA shut-off at 42 degrees C as 2S142. Thus, the elevated ppGpp levels in this mutant do not appear to be directly responsible for the cessation of rRNA synthesis at 42 degrees C.