Bacteria resort to all kind of intricate strategies to cope with changes in the outside world. For instance, the expression of the main outer membrane proteins is regulated by small RNA molecules, which do not encode for proteins. These small RNAs are in turn regulated by the activity of RNA-degrading enzymes. Researchers from the Control of Gene Expression Lab at ITQB have now uncovered the regulation of one such small RNAs in the pathogenic bacterium Salmonella typhimurium, pointing to a gene silencing mechanism similar to that of higher organisms. The work is published in Nucleic Acids Research.
Small RNAs bind specifically to messenger RNAs (the ones encoding proteins) to trigger their degradation and thus control protein expression. This story revolves around MicA, a small non-coding RNA of about 70 nucleotides, involved in the regulation of the bacterial envelope composition. Researchers now find that the fine tuning of MicA requires mainly two ribonucleases; while RNase E degrades isolated MicA molecules, RNase III degrades MicA bound to its target.
Proteins similar to RNase III are major actors in RNA regulation in eukaryotes (higher organisms). In a process known as RNA interference or gene silencing, small RNAs bind to the RNA of specific target genes, promoting their degradation and impeding the production of the respective protein. The fact that, in Salmonella, MicA is cleaved by RNase III in a target-dependent fashion, with the concomitant decay of the mRNA target, strengthens the RNase III role in the regulation of gene expression, also in the bacteria.
Nucl. Acids Res. (2010) doi: 10.1093/nar/gkq1239
Regulation of the small regulatory RNA MicA by ribonuclease III: a target-dependent pathway
Sandra C. Viegas, Inês J. Silva, Margarida Saramago, Susana Domingues and Cecília M. Arraiano