Enzyme localisation and collaboration in Staphylococcus aureus RNA decay
Peter REDDER - Department of microbiology and molecular medicine, Geneva University (Geneva, Swiss)
Invited by Reynald GILLET
RNA decay is an integral step in gene regulation, since the level of a given RNA at a given time is dependent on both its rate of transcription AND on its particular rate of degradation. This is especially true for bacteria, where typical mRNA half-lives range between 1 and 10 minutes, indicating that RNA turnover is a vigorous process in these organisms.
However, even in these short timeframes, there are large differences between the half-lives of various mRNAs. Therefore, in order to understand gene regulation, it is vital to understand the factors that target some RNA species for rapid degradation and the factors that protect other RNA species from decay.
In Staphylococcus aureus, a feared opportunistic pathogen, defects in the RNA decay machinery cause changes in quorum-sensing and to loss of virulence. RNases Y, J1 and J2 are three key components of this machinery, in addition to performing defined steps in the maturation of stable non-coding RNAs such as 16S rRNA and RNase P RNA. The paralogs RNase J1 and J2 form a complex with 5’ to 3’ exoribonuclease activity, where only RNase J1 is enzymatically active, although RNase J2 is essential in a structural role. RNase Y is an endoribonuclease, and while it is evolutionarily unrelated to RNase E from Escherichia coli, it is equally membrane anchored, and was until recently thought to be the major initiator of RNA decay, by providing access-points for exonucleolytic degradation by the RNase J1+J2 complex and the various 3’to 5’ exoribonucleases.
However, by examining the half-lives of individual RNA molecules on a global scale, in wild-type and RNase Y mutant strains, we have found that RNase Y is only rate-limiting for the turnover of the transcripts that encode about a hundred proteins. While this is still a sizable percentage of the S. aureus transcriptome, it is far from the apparently universal activity of RNase E, and it is clear that RNase Y must be able to select its targets. A global search for RNase Y cleavage sites provided a partial explanation, when it revealed a strong sequence preference near the 99 identified cleavage sites, although we suspect that both secondary structure of the RNA and sub-cellular localization of RNase Y are important additional elements in liming the RNase Y activity. The latter was especially highlighted when the release of RNase Y from its confinement to the membrane could complement both the cold-sensitivity and quorum-sensing defects caused by the deletion of the main RNA helicase in the decay-machinery. Currently we are investigating which factors initiate RNA-decay in an RNase Y independent manner, and how these mechanisms are controlled, with particular focus on RNases J1 and J2.
>> Thursday, June 30, at 11:30 - IGDR conference room (ground floor of Building 4 / Villejean Campus)
Seminar in English, free entry subject to availability