Regulation of Streptococcus gordonii sspB by the sspA gene product

Streptococcus gordonii expresses two related adhesins, SspA and SspB, the genes for which are adjacent on the chromosome and are regulated independently. Although the adhesins are functionally similar, the sspA promoter is more active than that of sspB. In this study we show an additional role for SspA in the control of sspB activity. Gel shift and DNA footprinting assays demonstrate that the SspA protein binds to the sspB promoter and protects a region 233 to 264 bp upstream of the predicted -35 promoter element. The responsiveness of the sspB promoter to SspA was investigated with a promoter-cat reporter. Expression of the sspB promoter was reduced by over 60% in an SspA-deficient mutant of S. gordonii. These results indicate that expression of S. gordonii sspB is positively regulated by the sspA gene product.