ctsR of Lactococcus lactis encodes a negative regulator of clp gene expression

Bacteria undergo a complex programme of differential gene expression in res ponse to stress. In Bacillus subtilis, it was recently shown that CtsR, a n egative transcriptional regulator, mediates stress-induced expression of co mponents of the Clp protease complex. In this study, a gene was identified in the Gram-positive bacterium Lactococcus lactis that encodes a 17 kDa pro duct with 38% identity to the CtsR protein of B. subtilis, By Northern anal yses it was found that in a L. lactis strain carrying a large internal dele tion of ctsR, including the region encoding a putative helix-turn-helix mot if, the amounts of clpC, clpP, clpB and clpE mRNAs were increased 3-8-fold compared to those present in wild-type L. lactis MG1363. In another ctsR mu tant strain in which only one-third of CtsR was deleted, leaving the putati ve DNA-binding domain and the C-terminal 29 amino acids intact, only minor derepression of clp gene expression was observed and, furthermore, all the clp genes were still induced by heat. These results indicate that the amino acids of CtsR involved in temperature sensing are located either close to the DNA-binding domain or in the C-terminal part of the protein. Thus, in L . lactis in addition to B. subtilis, CtsR is a key regulator of heat-shock- induced gene expression, suggesting that the presence of CtsR-homologous DN A-binding sites observed in many Grampositive bacteria reflects functional heat-shock regulatory systems.