Regulation of the small regulatory RNA MicA by ribonuclease III: a target-dependent pathway.
MicA is a trans-encoded small non-coding RNA, which downregulates porin-expression in stationary-phase. In this work, we focus on the role of endoribonucleases III and E on Salmonella typhimurium sRNA MicA regulation. RNase III is shown to regulate MicA in a target-coupled way, while RNase E is responsible for the control of free MicA levels in the cell. We purified both Salmonella enzymes and demonstrated that in vitro RNase III is only active over MicA when in complex with its targets (whether ompA or lamB mRNAs). In vivo, MicA is demonstrated to be cleaved by RNase III in a coupled way with ompA mRNA. On the other hand, RNase E is able to cleave unpaired MicA and does not show a marked dependence on its 5' phosphorylation state. The main conclusion of this work is the existence of two independent pathways for MicA turnover. Each pathway involves a distinct endoribonuclease, having a different role in the context of the fine-tuned regulation of porin levels. Cleavage of MicA by RNase III in a target-dependent fashion, with the concomitant decay of the mRNA target, strongly resembles the eukaryotic RNAi system, where RNase III-like enzymes play a pivotal role.
Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, Apartado 127, 2781-901 Oeiras, Portugal.
Sandra C
SC
Viegas
Inês J
IJ
Silva
Margarida
M
Saramago
Susana
S
Domingues
Cecília M
CM
Arraiano
D001425:Bacterial Outer Membrane Proteins / Q000378:metabolism; D020029:Base Pairing; D009154:Mutation; D012333:RNA, Messenger / Q000737:chemistry / Q000378:metabolism; D058727:RNA, Small Untranslated / Q000032:analysis / Q000737:chemistry / Q000378:metabolism*; D043244:Ribonuclease III / Q000235:genetics / Q000378:metabolism*; D012486:Salmonella typhimurium / Q000201:enzymology* / Q000235:genetics
D001425:Bacterial Outer Membrane Proteins; D012333:RNA, Messenger; D058727:RNA, Small Untranslated; C078167:OMPA outer membrane proteins; D043244:Ribonuclease III