Expression of Herpes Simplex Virus Type 1 and Type 2 Glycoprotein D Genes Using the Escherichia Coli lac Promoter

Summary

DNA fragments encoding herpes simplex virus type 1 and type 2 glycoprotein D (gD-1 and gD-2, respectively) have been inserted into plasmid vectors and expressed under the transcriptional control of the Escherichia coli lac promoter-operator. The proteins expressed in this system comprised gD sequences fused to a small bacteriophage λ Cro leader (i.e. Cro-gD). Such Cro-gD fusion proteins were found to be intrinsically unstable in E. coli and accumulated to low levels only. We found that fusion of this Cro-gD coding sequence to the 5′ end of a sequence encoding β-galactosidase (β-gal), resulted in high levels of synthesis of Cro-gD-β-gal fusion proteins provided that certain carboxy-terminal gD coding sequences were deleted. These Cro-gD-β-gal proteins accumulated to levels comprising approximately 10% of the total cell protein and were found to form intracellular insoluble aggregates. Insertion of an in-phase amber nonsense codon between the gD and β-gal coding sequences, resulted in synthesis of both Cro-gD and Cro-gD-β-gal proteins in cells containing suppressors. Under these conditions, the Cro-gD amber fragment was stabilized by the Cro-gD-β-gal protein. Chimaeric gD-1 and gD-2 containing proteins were found to be immunologically active and induced antibodies in rabbits which immunoprecipitated authentic gD polypeptides and neutralized the infectivity of both virus types.