ABSTRACT
In Escherichia coli, ribonucleases are effectors that rapidly modulate the levels of mRNAs for adaptation to a changing environment. Factors involved in the regulation of these ribonucleases can be relevant for mRNA stability. RNase II is one of the main ribonucleases responsible for exonucleolytic activity in E. coli extracts. We have identified and characterized a new E. coli gene, which was named gmr (gene modulating RNase II). The results demonstrate that a deletion of gmr can be associated with changes in RNase II levels and activity. Western analysis and exoribonuclease activity assays showed a threefold increase in RNase II in the gmr deletion strain. Gmr does not affect RNase II mRNA, but modulates RNase II at the level of protein stability. RNase II protein turnover is slower in the gmr deletion strain. We also show that RNase II levels change in different media, and that this regulation is abolished in a strain lacking gmr. The data presented here show that the regulation of ribonucleolytic activity can depend on growth conditions, and this regulation can be mediated by factors that are not RNases.
Subject(s)
Bacterial Proteins/genetics , Escherichia coli Proteins , Escherichia coli/growth & development , Escherichia coli/genetics , Exoribonucleases/metabolism , Amino Acid Sequence , Bacterial Proteins/metabolism , Base Sequence , Cell Division/genetics , Culture Media , Escherichia coli/metabolism , Exoribonucleases/genetics , Gene Deletion , Gene Expression Regulation, Bacterial , Molecular Sequence Data , Promoter Regions, Genetic , Sequence AnalysisABSTRACT
PNPase and RNase II are the key regulatory exonucleases controlling mRNA decay in Escherichia coli. The rnb transcripts were found to proceed through the terminator and PNPase was found to be involved in the 3' to 5' degradation of rnb mRNA. Analysis of these longer 3' termini revealed that they are located in UA-rich regions. Comparison of single and double mutants suggested that PNPase and RNase II could have different roles in the degradation of these unstructured regions. We have shown that RNase II levels can vary over a fivefold range in haploid cells and that its expression depends on PNPase levels. PNPase-deficient strains were found to have a 2-2.5-fold increase in RNase II activity, while PNPase-overproducing strains reduced the rnb message and RNase II levels. Conversely, the amount of PNPase in the rnb deletion strain was approximately twofold higher than that in the wild-type strain. These observations suggest that the two main exonucleases are inter-regulated through a fine tuning mechanism. We discuss the implications of these results with regard to mRNA degradation and cell metabolism.
