Nucleotide sequence of γδ resolvase gene and demonstration that its gene product acts as a repressor of transcription

The related transposons γδ and Tn3 each encode an efficient site-specific recombination system essential for transposition^1,2. The recombination occurs at a particular site, res, located within the intercistronic region between the two divergently transcribed genes that are required for transposition². The product of one of these genes, resolvase, catalyses the recombination at res. Recently, in vitro site-specific recombination has been demonstrated using purified resolvase and a model substrate containing two res sites³. Genetic analysis of mutants in the γδ/Tn3 tnpR gene, which encodes the resolvase protein, suggested that resolvase regulates the frequency of transposition in addition to catalysing recombination^4-6. Analysis of element-encoded proteins in minicells indicated a direct effect of resolvase on the levels of the element-encoded transposase, as well as on its own expression⁷. Here we report the sequence of the gene encoding γδ resolvase and compare the predicted amino acid sequence with that of the functionally interchangeable Tn3 protein⁶. In addition, we have determined the sites at which transcription of the transposase and resolvase genes initiates in vitro and have demonstrated that purified resolvase protein specifically represses transcription of both transposition related genes in this in vitro transcription system.