MUTATIONS AFFECTING TRANSLATIONAL COUPLING BETWEEN THE REP GENES OF AN INCB MINIPLASMID

The nature of translational coupling between repB and repA, the overla pping rep genes of the IncB plasmid pMU720, was examined. Mutations in the start codon of the promoter proximal gene, repB, reduced the effi ciency of translation of both rep genes. Moreover, there was no indepe ndent initiation of repA translation in the absence of repB translatio n. The position of the repB stop codon was crucial for the efficient e xpression of repA, with the wild-type positioning being optimal. Trans lational coupling was found to be totally dependent on the formation o f a pseudoknot structure. A model which invokes formation of a pseudok not to facilitate initiation of repA is proposed.