A lethal mutation which affects the maturation of ribosomes

Abstract

A temperature sensitive mutant of Escherichia coli which fails to recover from prolonged carbon starvation, was found to be irreversibly killed by exposure to a nonpermissive temperature (43 degrees C), with a half-life of about half an hour. This bacteriocidal effect of the temperature could be reversed by a number of antibiotics which block protein synthesis but not by blocking DNA synthesis. At the nonpermissive temperature, RNA and the protein synthetic capacities decrease before the DNA synthetic capacity is decreased. Analysis of ribosomal proteins and methylation of them did not reveal any consistent differences between the parental and mutant strains. Analysis of the ribosomal RNA revealed that it is being synthesized in similar amounts as in the parental strain at the nonpermissive temperature, however, after chase its level is decreased. Moreover, the 17S precursor RNA is slow to mature to 16S rRNA in the mutant strain at the nonpermissive temperature. Thus, these studies suggest that the mutation studied here affects a late maturation step in the synthesis of the rRNA. Therefore the gene is designated rimH (for ribosomal modification). All the properties bestowee on the mutant strain are caused by a single pleiotropic mutation which maps at min 14 of the E. coli map. Three point transduction crosses suggest the order rimH, leuS, RNA, LIP. This gene maps outside the two known clusters for ribosomal structural genes.