Cloning and expression in Escherichia coli of the sucrase gene from Bacillus subtilis

A recombinant cosmid carrying the sucrase gene (sacA) was obtained from a colony bank of E. coli harboring recombinant cosmids representative of the B. subtilis genome. It was shown that the sacA gene is located in a 2kb EcoRI fragment and that the cloned sequence is homologous to the corresponding chromosomal DNA fragment. A fragment of 2kb containing the gene was subcloned in both orientations in the bifunctional vector pHV33 and expression was further looked for in B. subtilis and E. coli. Complementation of a sacA mutation was observed in Rec+ and REc- strains of B. subtilis. Expression of sucrase was also demonstrated in E. coli, which is normally devoid of this activity, by SDS-polyacrylamide gel electrophoresis, specific immunoprecipitation and assay of the enzyme in crude extracts. The specific activity of the enzyme depended on the orientation of the inserted fragment. The saccharolytic activity was found to be cryptic in E. coli since the presence of the recombinant plasmids did not allow the transport of [U14C] sucrose and the growth of the cells. It was shown also that the recombinant cosmid contained part of the neighboring locus (sacP) which corresponds to a component of the PEP-dependent phosphotransferase system of sucrose transport of B. subtilis.