Intermolecular recombination of the herpes simplex virus type 1 genome analysed using two strains differing in restriction enzyme cleavage sites.

Intermolecular recombination of herpes simplex virus type 1 (HSV-1) was studied by analysing the segregation of strain-specific restriction enzyme cleavage sites among progeny viruses produced after co-infection by two HSV-1 strains differing in eight restriction enzyme cleavage sites. Out of 93 progeny viruses examined, 51 clones were recombinant, and crossover sites of the recombinants were mapped on the HSV-1 genome. These sites were distributed evenly in the unique sequence of the L component (UL) and the recombination frequency in UL was estimated to be 1.12 per genome length, or 0.007 per kilobase pair. No evidence was obtained to support the existence of enhanced intermolecular recombination events in the regions containing inverted repeats and the L-S junction in comparison with the recombination frequency in UL. The finding of recombinants in an arrangement that minimized the number of crossover events suggested the participation of both of two arrangements of the L component of parental DNA (P or IS, and IL or ISL) in the generation of the recombinants. The possibility of a preference for P or IS over IL or ISL arrangements remains to be determined.