Expression and regulation of the lactose transposon Tn951 in Rhizobium spp.

Abstract The expression of β-galactosidase by the lac transposon Tn 951 , in Escherichia coli , was found to be cAMP-dependent. This finding provided the basis for an investigation of the effect of cAMP on Tn 951 lac expression in Rhizobium , with the ultimate aim of using the Tn 951 system as a specific probe for cAMP mediated catabolite repression. When introduced into Rhizobium , Tn 951 directed the synthesis of β-galactosidase, which was inducible by isopropyl-β- d -thiogalactopyranoside (IPTG). Marked quantitative and qualitative differences in β-galactosidase expression were found between R. meliloti and R. japonicum during the growth cycle, with expression being higher in the former. β-Galactosidase levels were, however, unaffected by exogenous cAMP under catabolite repressing conditions.