Consequences of losing ribonuclease III on theEscherichia coli cell

Abstract

An isogenic pair ofEscherichia coli strains, one carrying anrnc ⁺ and the other anrnc ⁻ allele (a mutation which reduces the level of ribonuclease III), was compared. Thernc ⁻ strain fails to grow at very elevated temperatures (forE. coli) while thernc ⁺ strain does grow exponentially. Assaying the residual RNase III, like activity in extracts of thernc ⁻ strain at different pHs and at different temperatures suggested that this residual RNase III like activity is not due to RNase III. This raised the possibility that thernc ⁻ strain is devoid of any RNase III activity in the cell. Comparing the decay of newly synthesized RNA and functional decay of β-galactosidase mRNA in such strains revealed that in both strains these parameters proceed in similar rates, which suggests that RNase III is not involved in the metabolism of mRNA. During carbon starvation preexisting total RNA, as well as 23S and 16S rRNA, decay faster in thernc ⁻ strain, thus eliminating the possibility that RNase III is the endoribonuclease which initiates the decay of rRNA during starvation (Kaplan and Apirion, 1975a).