Regulation of Staphylococcus xylosus xylose utilization genes at the molecular level.

We have investigated the regulation of the operon encoding xylose utilization in Staphylococcus xylosus C2a and Staphylococcus carnosus TM300. For in vivo studies, transcriptional fusions of the xylAB regulatory region to the lipase gene from Staphylococcus hyicus were constructed. Repression of lipase activity depended on a functional xylR gene and an xyl operator palindrome downstream of the promoter, while induction was obtained in the presence of xylose. Inactivation of either xylR or the xyl operator led to constitutive expression in the absence of xylose. Crude protein extracts from xylR+ staphylococci led to gel mobility shifts of the xyl regulatory DNA in the absence but not in the presence of xylose. A copper-phenanthroline footprint of the shifted band revealed protection of 28 phosphodiesters from cleavage in each strand of the xyl operator. Thus, the Xyl repressor covers the DNA over more than 2.5 helical turns. Glucose repression of the xyl operon occurs at the level of transcription and is independent of a functional xylR gene. A potential cis-active sequence element for glucose repression is discussed on the basis of sequence similarities to respective elements from bacilli.