PREFERENTIAL CIS ACTION OF IS-10 TRANSPOSASE DEPENDS UPON ITS MODE OFSYNTHESIS

A number of bacterial DNA-binding proteins, including IS element trans posases, act preferentially in cis. We show below that the degree of p referential cis action by IS10 transposase depends upon its mode of sy nthesis at steps subsequent to transcription initiation. Cis preferenc e is increased several fold by mutations that decrease translation ini tiation, by the presence of IS10-specific antisense RNA and by plasmid s that increase the level of cellular RNases. Conversely, cis preferen ce is decreased by mutations that increase translation initiation; in some cases, cis preference is nearly abolished. Mutations that alter t he rate of transcription initiation have no effect. In light of other observations, we suggest that cis preference is strongly dependent upo n the rate at which transcripts are released from their templates and/ or the half-life of the transposase message. These observations provid e further evidence that inefficient translation plays multiple roles i n the biology of IS10.