MOLECULAR CHARACTERIZATION OF THE GENE ENCODING AN 18-KILODALTON SMALL HEAT-SHOCK PROTEIN ASSOCIATED WITH THE MEMBRANE OF LEUCONOSTOC-OENOS

In Leuconostoc oenos, different stresses such as heat, ethanol, and ac id shocks dramatically induce the expression of an 18-kDa small heat s hock protein called Lo18, The corresponding gene (hsp18) was cloned fr om a genomic library of L. oenos constructed in Escherichia coli. A 2. 3-kb DNA fragment carrying the hspl8 gene was sequenced, The hspl8 gen e encodes a polypeptide of 148 amino acids with a calculated molecular mass of 16,938 Da, The Lo18 protein has a significant identity with s mall heat shock proteins of the alpha-crystallin family, The transcrip tional start site was determined by primer extension. This experiment allowed us to identify the promoter region exhibiting high similarity to consensus promoter sequences of gram-positive bacteria, as well as E. coli. Northern blot analysis showed that hsp18 consists of a unique transcription unit of 0.6 kb. Moreover, hspl8 expression seemed to be controlled at the transcriptional level. This small heat shock protei n was found to be peripherally associated with the membrane of L. oeno s.