Gin-mediated site-specific recombination in bacteriophage Mu DNA: overproduction of the protein and inversion in vitro.

Inversion of the G segment in bacteriophage Mu DNA occurs by a site-specific recombination event and determines the host specificity of Mu phage particles produced. Inversion is mediated by a Mu function (Gin). The gin gene has been placed under control of the inducible lambda pL promoter and a synthetic Shine-Dalgarno linker upstream of the initiation codon. The Gin protein content in induced cells is boosted to 10% of total protein. Partially purified extracts from overproducing strains promote efficient inversion of the G DNA segment in vitro which is visualized by agarose gel electrophoresis of the substrate DNA after cutting with appropriate restriction endonucleases. The in vitro reaction requires Mg, a super-coiled DNA substrate and occurs in the absence of exogenous ATP. Inversion from the G(+) to the G(-) orientation is as efficient as the switch from G(-) to G(+).