ROLE OF LA PROTEASE IN NEGATIVE CONTROL OF VIBRIO-FISCHERI LUXICDABE GENE-EXPRESSION IN ESCHERICHIA-COLI

The Escherichia coli La protease [EC 3.4.21.53] specifically inhibits activity of the regulatory protein LuxR, a positive transcription acti vator of the luxlCDABE rightward operon of the lux regulon of marine b acteria Vibrio fischeri. Cells of the Escherichia coli strain AB 1899 lon 1 comprising the entire lux regulon display very intense biolumine scence, with no lag period in the induction curve characteristic of lo n(+) strains. Transformation of lon1 cells with plasmid pBRlon carryin g the active lonA gene reduces luminescence by several orders of magni tude and considerably increases the induction lag period. On the contr ary, with a lon(+) strain as a host, hybrid plasmids pAL-1 and pT7-1 e ncoding specific antilon and parlon transcripts that inhibit translati on of La protease cause a considerable increase in bioluminescence and abolishment of the lag. It is assumed that protein LuxR is the target for La protease, since addition of equal amounts of the autoinducer t o lon(+) AB1157 (pAC16) and AB1157 (pAC16, pBRlon) strains affects the luminescence induction curve to a greater extent when plasmid pBRlon is absent.