A decreased level of FtsZ is responsible for inviability of RNase E-deficient cells

The endoribonuclease RNase E, encoded by the essential gene rne, plays a major role in cellular RNA metabolism, i.e. maturation of functional RNAs such as rRNA and tRNA, degradation of many mRNAs and processing of the ftsZ mRNA which encodes the essential cell division protein FtsZ. RNase E function is somehow regulated by the RNA binding protein Hfq. We found that temperature-sensitive colony formation of a rne-1 mutant was partially suppressed by introduction of a hfq::cat mutation. Neither accumulation of rRNA and tRNA(Phe) precursors nor incomplete processing of ftsZ mRNA in the rne-1 mutant was rescued by the hfq::cat mutation. However, the amount of FtsZ protein that was decreased in the rne-1 mutant was recovered up to a level similar to that of wild-type cells by the hfq::cat mutation. Overproduction of Hfq inhibited cell division because of decreased expression of FtsZ. Artificial expression of the FtsZ protein from a plasmid-borne ftsZ gene partially suppressed the temperature-sensitivity of the rne-1 mutant. These results suggest that the decreased level of FtsZ is, at least in part, responsible for the inviability of RNase E-deficient cells.