A GENETIC SYSTEM THAT REPORTS TRANSIENT ACTIVATION OF GENES IN BACILLUS

Site-specific recombination is a powerful tool for precise excision of DNA fragments. We used this characteristic to construct a genetic sys tem to report the transient activation of a promoter by promoting the stable acquisition of an antibiotic resistance marker by the bacterium . The system is composed of two compatible plasmid derivatives from Gr am-positive bacteria. One of the plasmids allows the insertion of prom oters upstream from tnpI, which encodes the site-specific recombinase of Tn4430. The second plasmid carries two selectable resistance genes: one is flanked by two site-specific recombination sequences and is lo st following recombination; in contrast, the other resistance gene bec omes functional after the site-specific recombination event. By insert ing conditionally controlled promoters (the xylose-inducible xylA prom oter or the plcA promoter whose expression is dependent on the growth medium) upstream of tnpI, we demonstrated that our genetic system resp onds to signals inducing transcription by conferring a new resistance phenotype to the host bacteria. Thus, this system can be used to ident ify genes which are transiently or conditionally expressed. (C) 1997 E lsevier Science B.V.