RNA thermometers are common in α- and γ-proteobacteria

Abstract

AbstractExpression of many rhizobial small heat-shock genes is controlled by the ROSE element, a thermoresponsive structure in the 5′-untranslated region of the corresponding mRNAs. Using a bioinformatics approach, we found more than 20 new potential ROSE-like RNA thermometers upstream of small heat-shock genes in a wide variety of α- and γ-proteobacteria. Northern blot analyses revealed heat-inducible transcripts of the representative candidateCaulobacter crescentus CC2258,Escherichia coli ibpAandSalmonella typhimurium ibpAgenes. Typical σ32-type promoters were mapped upstream of the potential RNA thermometers by primer extension. Additional translational control was demonstrated in alacZreporter system and by site-directed mutagenesis. RNA secondary structure predictions strongly suggest that the Shine-Dalgarno sequence in the RNA thermometers is masked at low temperatures. Combining two regulatory modules, a σ32promoter and a ROSE-type RNA thermometer, provides a novel stringent mechanism to control expression of small heat-shock genes.