A second operator is involved in Pseudomonas aeruginosa elastase (lasB) activation

Pseudomonas aeruginosa LasB elastase gene (lasB) transcription is controlled hy the two-component quorum-sensing system of LasR, and the autoinducer, 3OC(12)-NSL (N-3-[oxododecanoyl] homoserine lactone). LasR and 3OC(12)-HSL-mediated lasB activation requires a functional operator sequence (OP1) in the lasB promoter region, Optimal activation of lasB, however, requires a second sequence of 70% identity to OP1, named OP2, located 43 bp upstream of OP1, In this study, we used sequence substitutions and insertion mutations in lasBp-lacZ fusion plasmids to explore the role of OP2 in lasB activation. Our results demonstrate that (i) OP1 and OP2 synergistically mediate lasB activation; (ii) OP2, like OP1, responds to LasR and 30C(12)-HSL; and (iii) the putative autoinducer-binding domain of LasR is not required for synergistic activation from OP1 and OP2.