Transfer of UL41, the gene controlling virion-associated host cell shutoff, between different strains of herpes...

Studies with mutant viruses have suggested that the product of gene UL41 of herpes simplex virus type 1 (HSV-1) controls the virion-mediated inhibition of cellular protein synthesis as well as the rate of degradation of viral mRNAs. HSV-1 strain 17+ has a weak host shutoff function, whereas HSV-2 strain G shuts off strongly. A gene of HSV-2(G), judged from its position in the genome to be the probable analogue of gene UL41 of HSV-1, was inserted into the nonessential thymidine kinase gene of HSV-1(17+). The recombinant virus, 17G41, exhibited a strong shutoff function and its immediate early mRNA did not accumulate in the presence of cycloheximide. It resembled HSV-2(G) in these respects and not the parent, confirming the function of the transferred gene. Recombinant virus 17G41 carries the UL41 genes of both strains, 17+ and G, and in this situation the strong shutoff function was dominant. However, after mixed infection with equal multiplicities of 17G41 and HSV-1(17+) the weak shutoff function was dominant. The recombinant, 17G41, was further modified by insertion of a lacZ expression cassette into the coding region of the original gene UL41 (17+). The resulting virus, 17(41-)G41, also had a strong shutoff activity but grew poorly in tissue culture.