Expression of BrpA in Streptococcus mutans is regulated by FNR‐box mediated repression. (24th August 2017)

• Record Type: Journal Article
• Authors: Liao, S.; De, A.; Thompson, T.; Chapman, L.; Bitoun, J.P.; Yao, X.; Yu, Q.; Ma, F.; Wen, Z.T.
• Is Part Of: Molecular oral microbiology. Volume 32:Number 6(2017)
• Page Start: 517
• Page End: 525
• Publication Date: 2017-08-24
• Subjects: biofilms -- BrpA -- fumarate‐nitrate reductase regulator -- gene expression -- LytR‐CpsA‐Psr proteins -- Streptococcus mutans; Mouth -- Microbiology -- Periodicals; Respiratory infections -- Microbiology -- Periodicals; Mouth -- Diseases -- Immunological aspects -- Periodicals; 617.522
• DOI: 10.1111/omi.12193
• Languages: English
• ISSNs: 2041-1006

Abstract

Summary: Our previous studies showed that brpA in Streptococcus mutans, which encodes a member of the LytR‐CpsA‐Psr family of proteins, can be co‐transcribed with brpB upstream as a bicistronic operon, and the intergenic region also has strong promoter activity. To elucidate how brpA expression is regulated, the promoter regions were analyzed using polymerase chain reaction‐based deletions and site‐directed mutagenesis and a promoterless luciferase gene as a reporter. Allelic exchange mutagenesis was also used to examine genes encoding putative trans‐ acting factors, and the impact of such mutations on brpA expression was analyzed by reporter assays. Multiple elements in the short brpA promoter (nucleotide −1 to −344 relative to start cordon ATG) were shown to have a major impact on brpA expression, including an FNR‐box, for a putative binding site of an FNR‐type of transcriptional regulator. When compared with the intact brpA promoter, mutations of the highly conserved nucleotides in FNR‐box from TTGATgtttAcCtt to TTACA gaaaGtTac resulted in 1362‐fold increases of luciferase activity ( P < .001), indicative of the FNR‐box‐mediated repression as a major mechanism in regulation of brpA expression. When luciferase reporter was fused to the upstream brpBA promoter (nucleotides −784 to −1144), luciferase activity was decreased by 4.5‐fold ( P < .001) in the brpA mutant, TW14D, and by 67.7‐fold ( P < .001) in the brpB mutant, JB409, compared with the wild‐type, UA159. However, no such effects were observed when the reporter gene was fused to the short brpA promoter and its derivatives. These results also suggest that brpA expression in S. mutans is auto‐regulated through the upstream brpBA promoter.