Regulated high-level expression of the Herpes simplex type I thymidine kinase gene in Escherichia coli.

A plasmid-borne Herpes simplex virus type 1 (HSV-1) thymidine kinase (TK) gene (tk) was expressed in Escherichia coli by inserting a 203-bp lacL8/UV5 promoter-operator segment, in frame, 53 bp 5' to the native tk translational start codon. The hybrid gene created by this fusion encodes a polypeptide which has 25 additional amino acids on the amino terminus of the HSV-1 TK protein and phenotypically complements a tdk- mutation of E. coli. This fusion polypeptide has been characterized by maxicell, immunoprecipitation, and native gel techniques, and its activity is inhibited by anti-HSV-1 antibody. In a tk expressor strain containing a F' lacIq (which overproduces the lactose repressor), the isopropyl-beta-D-thiogalactoside (IPTG) causes greater than 1000-fold coordinate induction of the plasmid-encoded TK and chromosomal beta-galactosidase activities. Pulse-chase induction demonstrates the fused TK polypeptide to be as stable as beta-galactosidase. HSV-1 tk-specific RNA isolated from this bacterial strain has a short half-life characteristic of bacterial messages.