Premium
A small RNA downregulates LamB maltoporin in Salmonella
Author(s) -
Bossi Lionello,
FigueroaBossi Nara
Publication year - 2007
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/j.1365-2958.2007.05829.x
Subject(s) - biology , operon , salmonella enterica , sigma factor , downregulation and upregulation , bacterial outer membrane , lac operon , microbiology and biotechnology , escherichia coli , gene , gene expression , genetics , promoter
Summary In Escherichia coli and Salmonella enterica , activation of σ E ‐dependent envelope stress response leads to the abrupt decline in the synthesis of all major outer membrane proteins (OMPs). Recent studies found that two σ E ‐controlled small RNAs (sRNAs), MicA and RybB, downregulate a number of OMPs. While RybB targets several different mRNAs, including ompC and ompD , MicA was up to date thought to act solely on ompA . Here we present evidence showing that MicA downregulates a second Salmonella OMP: LamB maltoporine. In strains overexpressing σ E , MicA accumulation leads to a significant decrease in LamB protein and mRNA levels, as well as a reduction in β‐galactosidase activity in a strain carrying a lamB–lacZ translational fusion. The latter findings provided the basis for a genetic screen that allowed isolating point mutations in the micA gene and in its σ E promoter. All alleles obtained displayed their altered regulatory phenotype from their natural chromosomal location. LamB downregulation by MicA requires a functional Hfq protein. Besides this role, confined to σ E ‐activated conditions, we show that loss of Hfq results in the accumulation of a lamB‐malM dimeric precursor and of malM mRNA during unchallenged growth. This suggests that Hfq normally intervenes in a mechanism that uncouples expression of the malK‐lamB‐malM operon, causing the distal portion of the transcript to be clipped off and degraded.