MOLECULAR CHARACTERIZATION OF A STRESS-INDUCIBLE GENE FROM LACTOBACILLUS-HELVETICUS

A gene (htrA) coding for a stress-inducible HtrA-like protein from Lac tobacillus helveticus CNRZ32 was cloned, sequenced, and characterized. The deduced amino acid sequence of the gene exhibited 30% identity wi th the HtrA protein from Escherichia coli; the putative catalytic tria d and a PDZ domain that characterize the HtrA family of known bacteria l serine proteases were also found in the sequence, Expression of the L. helveticus htrA gene in a variety of stress conditions was analyzed at the transcriptional level. The strongest induction, resulting in o ver an eightfold increase in the htrA transcription level, was found i n growing CNRZ32 cells exposed to 4% (wt/vol) NaCl. Enhanced htrA mRNA expression was also seen in CNRZ32 cells after exposure to puromycin, ethanol, or heat. The reporter gene gusA was integrated in the Lactob acillus chromosome downstream of the htrA promoter by a double-crossov er event which also interrupted the wild-type gene. The expression of gusA in the stress conditions tested was similar to that of htrA itsel f. In addition, the presence of an intact htrA gene facilitated growth under heat stress but not under salt stress.