MqsR, a Crucial Regulator for Quorum Sensing and Biofilm Formation, Is a GCU-specific mRNA Interferase in Escherichia coli

Abstract

The mqsR gene has been shown to be positively regulated by the quorum-sensing autoinducer AI-2, which in turn activates a two-component system, the qseB-qseC operon. This operon plays an important role in biofilm formation in Escherichia coli. However, its cellular function has remained unknown. Here, we found that 1 base downstream of mqsR there is a gene, ygiT, that is co-transcribed with mqsR. Induction of mqsR caused cell growth arrest, whereas ygiT co-induction recovered cell growth. We demonstrate that MqsR (98 amino acid residues), which has no homology to the well characterized mRNA interferase MazF, is a potent inhibitor of protein synthesis that functions by degrading cellular mRNAs. In vivo and in vitro primer extension experiments showed that MqsR is an mRNA interferase specifically cleaving mRNAs at GCU. The mRNA interferase activity of purified MqsR was inhibited by purified YgiT (131 residues). MqsR forms a stable 2:1 complex with YgiT, and the complex likely functions as a repressor for the mqsR-ygiT operon by specifically binding to two different palindromic sequences present in the 5-untranslated region of this operon.

Regulation of phenotypic variability by a threshold-based mechanism underlies bacterial persistence

“…Threshold regulation of phenotypic variability may be a general property of those motifs, whose function would be to differentiate bacterial populations into distinct subpopulations to cope with stress (21). Recent evidence that implicates TA modules in Myxococcus development (43) and in biofilm formation (44,45) support that view. Finally, through linking a genetic regulatory motif and its phenotypic effect, we now have a basic understanding of the connections between multiple elements of bacterial persistence: genotype, phenotype, and fitness.…”

Structure of the Escherichia coli Antitoxin MqsA (YgiT/b3021) Bound to Its Gene Promoter Reveals Extensive Domain Rearrangements and the Specificity of Transcriptional Regulation

“…Recently, we determined the crystal structures of MqsA alone and the MqsR⅐MqsA complex and showed that the mqsRA operon defines a novel family of TA systems in E. coli, in which MqsR is the toxin and MqsA is the antitoxin (19). The structure revealed that the MqsR toxin is a ribonuclease belonging to the RelE bacterial toxin family (19,34,35). MqsR is unique because it is the first toxin linked to biofilms and quorum sensing (33) and is the first toxin that, when deleted, decreases persister cell formation (31).…”

“…The antitoxin MqsA is even more unusual because it is the first antitoxin that requires a metal, zinc, for structural stability (19); it is the only E. coli antitoxin that is structured throughout its entire sequence; and it is the first antitoxin demonstrated to bind DNA via its C-terminal and not N-terminal domain (19, 27, 36 -39). Critically, in addition to binding its own promoter (19,34,35,40), MqsA and the MqsR⅐MqsA complex are also the only known antitoxin/TA pair that bind not only their own promoter but also the promoters of other genes that play important roles in E. coli physiology, including mcbR and spy (19) as well as cspD (31). Moreover, although 14 antitoxin structures have been solved to date, their primary sequences are highly divergent when compared with MqsA (supplemental Table S1) because the sequence identity between MqsA and the most closely related antitoxin, the E. coli protein HigA, is only 13%.…”

Toxin Kid uncouples DNA replication and cell division to enforce retention of plasmid R1 in Escherichia coli cells

“…In view of all this, we argued that Kid and Kis functioned as a rescue system for plasmid R1, and not as a PSK system (24). This proposal cannot be supported by results elsewhere, suggesting that Kid may cleave mRNA at simpler UAH sites (with H being A, C, or U) (25,26), a view that has prevailed in the literature (14,16,(27)(28)(29). Moreover, other observations indicate that our past experiments may have been inappropriate to conclude that Kid does not kill Escherichia coli cells (30,31).…”

“…24 and below). Because the notion that Kid cleaves mRNAs at UA(A/C/U) (14,27), UA(A/C) (28), or UAC (16, 29) prevailed, we decided to investigate this issue in more detail. Resumption of cell growth in Fig.…”