Gene fusion vehicles for the analysis of gene expression in Rhizobium meliloti.

A set of plasmid cloning vehicles was developed to facilitate the construction of gene or operon fusions in Rhizobium meliloti. The vehicles also contain a broad-host-range replicon and could be introduced into bacteria either by transformation or by transduction, using bacteriophage P2. Insertion of foreign DNA into a unique restriction endonuclease cleavage site promotes the synthesis of either the Escherichia coli lactose operon or the kanamycin phosphotransferase gene from transposon Tn5. Expression of the lactose operon could be detected by observing the color of Rhizobium colonies on medium that contained a chromogenic indicator. We also determined the growth conditions that make it possible to select either for or against the expression of the E. coli lactose operon in R. meliloti. Recombinant plasmids were constructed by inserting MboI restriction fragments of R. meliloti DNA into one of the vehicles, pMK353 . Expression of beta-galactosidase by a number of these recombinants was measured in both R. meliloti and E. coli.