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Background: Escherichia coli rng gene (previously called cafA) encodes a novel RNase, named RNase G, which is involved in the 5 0 end-processing of 16S rRNA. In rng mutant cells, a precursor form of 16S rRNA, 16.3S rRNA, is accumulated. Here we report a role of RNase G in the in vivo mRNA metabolism.

We analyzed the functional relationship between the Escherichia coli RNase E and the CafA protein, which show extensive sequence similarity. The temperature-sensitive growth of the RNase E mutant strain ams1 was partially suppressed by multicopy plasmids bearing the cafA gene. Introduction of a cafA::cat mutation enhanced the temperature sensitivity of the ams1 mutant. These results suggest that there is a functional homology between these two proteins.

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The Escherichia coli RNase G is known as an endoribonuclease responsible for the 5'-end maturation of 16S rRNA and degradation of several specific mRNAs such as adhE and eno mRNAs. In this study, we found that an RNase G mutant derived from the MC1061 strain did not grow on a glucose minimal medium. Genetic analysis revealed that simultaneous defects of cra and ilvIH, encoding a transcriptional regulator of glycolysis/gluconeogenesis and one of isozymes of acetohydroxy acid synthase, respectively, were required for this phenomenon to occur. The results of additional experiments presented here indicate that the RNase G mutation, in combination with cra mutation, caused the increased production of pyruvic acid from glucose, which was then preferentially converted to valine due to the ilvIH mutation, resulting in depletion of isoleucine. In fact, the rng cra double mutant produced increased amount of pyruvate in the medium. These results suggest that the RNase G mutation could be applied in the breeding of producer strains of pyruvate and its derivatives such as valine.

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The Escherichia coli RNase E is an essential endoribonuclease involved in processing and/or degradation of rRNAs, tRNAs, and non-coding small RNAs as well as many mRNAs. It is known that RNase E activity is somehow regulated by an RNA-binding protein Hfq, at least in some cases. We searched for proteins that showed changes in expression in both hfq::cat and rne-1 mutant cells as compared with the wild type, and found that a protein band of 49-kDa decreased in these mutant cells at 42 degrees C, the restrictive temperature for rne-1. N-terminal amino acid sequencing identified it as a mixture of GadA and GadB, two isozymes of glutamate decarboxylase involved in glutamate-dependent acid resistance. The rne-1 mutant as well as the hfq mutant showed decreased survival under acidic conditions (pH 2.5). Hfq is known to regulate the expression of GadA/B in RpoS- and GadY small RNA-dependent ways. We examined the expression of these two regulators in rne-1 mutant cells. In the mutant cells, the induction of GadY was defective at 42 degrees C, but the expression of RpoS was normal. These results indicate that RNase E is required for induction of the glutamate-dependent acid resistance system in a RpoS-independent manner.