Tn5tac1, a derivative of transposon Tn5 that generates conditional mutations.

Conditional lethal mutations are valuable for analyzing essential genes. We describe here a derivative of the bacterial transposon Tn5 called Tn5tac1 and its use in an innovative strategy for making mutations with conditional phenotypes. The 4.6-kilobase Tn5tac1 element contains a strong, regulatable, outward-facing promoter (Ptac) near one end and is polar on the expression of distal genes when the inducer of Ptac [isopropyl beta-D-thiogalactoside (IPTG)] is absent. Our results show that two unusual conditional mutant phenotypes can result from Tn5tac1 insertion in Escherichia coli: one is corrected by IPTG while the other is induced by IPTG. The broad host range of Tn5 and the conditional nature of these mutant phenotypes makes Tn5tac1 well suited for identifying essential genes in diverse bacterial species.