Abstract
BackgroundThermal regulation of gene expression occurs in many microorganisms, and is mediated via several typical mechanisms. Yersinia pestis is the causative agent of the plague and spreads by zoonotic transfer from fleas to mammalian blood with a concomitant rapid temperature change, from ambient to 37 °C, which induces the expression of capsular antigen (Caf1) that inhibits phagocytosis. Caf1 is formed into long polymeric fimbriae by a periplasmic chaperone (Caf1M) and outer membrane usher (Caf1A). All three are encoded on an operon regulated by an AraC-type transcription factor Caf1R. The aim of this study was to determine the role of Caf1R in the thermal control of caf1 operon gene expression.ResultsPCR analysis of cDNA demonstrated that the genes of the operon are transcribed as a single polycistronic mRNA. Bioinformatic analysis, supported by deletion mutagenesis, then revealed a region containing the promoter of this polycistronic transcript that was critical for Caf1 protein expression. Caf1R was found to be essential for Caf1 protein production. Finally, RT-PCR analysis and western blot experiments showed large, Caf1R dependent increases in caf1 operon transcripts upon a shift in temperature from 25 °C to 35 °C.ConclusionsThe results show that thermal control of Caf1 polymer production is established at the transcriptional level, in a Caf1R dependent manner. This gives us new insights into how a virulent pathogen evades destruction by the immune system by detecting and responding to environmental changes.
Highlights
Thermal regulation of gene expression occurs in many microorganisms, and is mediated via several typical mechanisms
Microorganisms can employ a suite of different mechanisms to sense and respond to changes in temperature by altering their patterns of gene expression
The caf1 operon is transcribed as a polycistronic transcript In the caf1 operon, the caf1R coding sequence is on the opposite strand to, and separated by a 328 nucleotide intergenic region I, from the remaining genes, which are arranged with a very short (24 nt) intergenic region II between caf1M and caf1A and a larger intergenic region III of 80 nt between caf1A and caf1 (Fig. 1a)
Summary
Thermal regulation of gene expression occurs in many microorganisms, and is mediated via several typical mechanisms. Microorganisms can employ a suite of different mechanisms to sense and respond to changes in temperature by altering their patterns of gene expression These mechanisms can act at either the transcriptional or translational levels and can be mediated by protein, RNA or DNA [1]. Typical mechanisms include changes in the degree of supercoiling in DNA, as well as elements of local structure such as promoter curvature, which can affect transcription efficiency, when temperature increases or falls [1]. Another common mechanism involves RNA “thermometers” that form temperature dependent mRNA secondary structures that can inhibit translation below a critical temperature [1, 2]. Some proteins can undergo conformational changes in response to alterations in temperature, resulting in the post-translational modification of downstream transcription factors [3, 4], inhibition of DNA binding [5, 6], or protein degradation [7], with subsequent changes in gene expression
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