Extragenic suppressors of RNase E ts mutants
(English)Manuscript (preprint) (Other academic)
RNase E is an essential endoribonuclease and plays a central role in regulating mRNA levels and stable RNA activity in the bacterial cell. Previous studies of RNA half-life and processing in strains carrying rne mutations have shown that it is the catalytic half of RNase E that is essential for bacterial growth, but have not identified a specific reason for this essentiality. In this study we have used two ts mutations in the catalytic region of RNase E (rne-6 and rne-9) from Salmonella as tools to select and screen for extragenic suppressors of the temperature-sensitive phenotype. We reasoned that identifying extragenic suppressors might give information on the essential function of RNase E. 15 independent extragenic suppressors were isolated and mapped to three different loci on the Salmonella chromosome: rpsA (encoding ribosomal protein S1); vacB (encoding RNase R); and within and neighbouring the ORFs STM1551/1550, putatively encoding a toxin-antitoxin system similar to RelBE from E. coli. Each suppressor mutation could cross-suppress the ts phenotypes of rne-6 and rne-9 and each suppressor mutation alone was viable in a wild-type background. We discuss a model where at the non-permissive temperature an excess of mRNA (including defective species) may trap ribosomes non-productively, reducing the rate of protein synthesis and growth. Accordingly the rpsA mutation may suppress the ts phenotype by reducing the rate of translation initiation, and by default increasing the probability that residual RNase E activity turns over mRNA. The vacB mutations may expand the substrate range of RNase R allowing it to more efficiently substitute for poorly active RNase E in degrading mRNA. Finally, the mutations in the STM1551 region may increase the amount of RelE-like toxin and thereby increase the rate of mRNA turnover. This model makes predictions which can be experimentally tested.
rpsA; vacB; RNase R; RelBE; RNase E; mRNA turnover
Research subject Microbiology; Molecular Cellbiology
IdentifiersURN: urn:nbn:se:uu:diva-159662OAI: oai:DiVA.org:uu-159662DiVA: diva2:446167