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Autoregulation of the S. mutans SloR metalloregulator is constitutive and driven by an independent promoter

By Patrick Monette, Richard Brach, Annie Cowan, Roger Winters, Jazz Weisman, Foster Seybert, Kelsey Goguen, James Chen, Arthur Glasfeld, Grace Spatafora

Posted 14 Apr 2018
bioRxiv DOI: 10.1101/301416 (published DOI: 10.1128/JB.00214-18)

Streptococcus mutans, one of ~600 bacterial species in the human oral cavity, is among the most acidogenic constituents of the plaque biofilm. Considered to be the primary causative agent of dental caries, S. mutans harbors a 25kDa SloR metalloregulatory protein which controls metal ion transport across the bacterial cell membrane to maintain essential metal ion homeostasis. The expression of SloR derives, in part, from transcriptional readthrough of the sloABC operon which encodes a Mn2+/Fe2+ ABC transport system. Herein, we describe the details of the sloABC promoter that drives this transcription, as well as a novel independent promoter in an intergenic region (IGR) that contributes to downstream sloR expression. RT-PCR studies support sloR transcription that is independent of sloABC expression, and the results of 5' RACE revealed a sloR transcription start site in the IGR from which the -10 and -35 promoter regions were predicted. The results of gel mobility shift assays support direct SloR binding to the IGR, albeit with lower affinity than SloR binding to the sloABCR promoter. Function of the sloR promoter was validated in qRT-PCR experiments. Interestingly, sloR expression was not significantly impacted when grown in the presence of high manganese, whereas expression of the sloABC operon was repressed under these conditions. The results of in vitro transcription studies support SloR-mediated transcriptional-activation of sloR and -repression of sloABC. Taken together, these findings implicate SloR as a bifunctional regulator that represses sloABC promoter activity and encourages sloR transcription from an independent promoter.

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