6533b85cfe1ef96bd12bc6f6

RESEARCH PRODUCT

Sigma B-dependent regulatory sRNA Rli47 represses isoleucine biosynthesis in Listeria monocytogenes

subject

description

International audience; Background: Small regulatory RNAs (sRNAs) can influence cellular processes by targeting mRNAs, leading to translation inhibition and mRNA degradation. Previous studies have shown that the σB-dependent sRNA Rli47 is induced in L. monocytogenes stationary phase cells, in the intestinal lumen and macrophages, but its function has remained elusive. Objectives: This study aimed to comprehensively characterize Rli47 and determine its biological function in L. monocytogenes. Methods: Besides in silico predictions, several molecular approaches such as DMS-MaPseq, northern blotting, EMSAs, RTqPCR, RNA-seq and phenotypic experiments were applied. Results: Rli47 was shown to basepair through a single-stranded CU-rich loop with the ribosome binding site of ilvA mRNA, which encodes for threonine deaminase (TD), the first enzyme of the isoleucine biosynthetic pathway. Mutational analysis of the predicted binding regions on either Rli47 or ilvA mRNA abolished the basepairing. Rli47 was shown to reduce the expression of ilvA. A significantly shorter growth lag was found on Drli47 and DsigB than the wild-type in isoleucine-depleted medium. Moreover, TD activity was higher in both mutant strains under this condition. Complementary transcriptomic analysis identified complex changes in gene expression in the Drli47 mutant strain and highlighted a significant role for Rli47 in modulating amino acid metabolism. A potential role for Rli47 in the regulation of isoleucine biosynthesis emerged. Data point to a model where Rli47 is responsible for specifically repressing isoleucine biosynthesis even in conditions where it is absent, suggesting that isoleucine might act as a critical signal for L. monocytogenes at certain times during its life cycle.