EXPRESSION OF C5 PROTEIN, THE PROTEIN-COMPONENT OF ESCHERICHIA-COLI RNASE-P FROM THE TAC PROMOTER

The accurate function of C5 protein, the protein component of Escheric hia coil RNase P, is uncertain in vivo. A controllable expression syst em for C5 protein was constructed which can be used to investigate eff ects of C5 protein on various cellular functions including biosynthesi s of RNase P in vivo. The semisynthetic rnpA gene encoding C5 protein was fused to the tac promoter of the pKK223-3 expression vector. This tac promoter expression system produced a high level of C5 protein upo n induction with isopropyl-beta-D-thiogalacto-pyranoside. When the ove rexpressed C5 protein was purified and used for reconstitution of RNas e P, the reconstituted enzyme was active, The N-terminal amino acid of the overexpressed C5 protein was leucine specified by the second codo n of the rnpA gene. The more controllable expression system was constr ucted by introducing the lacI(q) gene into the vector sequence itself.