Either orientation of the L segment of the herpes simplex virus genome may participate in the production of viable intertypic recombinants.

We have analysed the genome structures of 90 recombinant viruses produced by co-infection of baby hamster kidney cells with the DNA of a herpes simplex virus type 1 temperature-sensitive mutant (tsD) and specific DNA fragments of wild-type herpes simplex virus type 2 at non-permissive temperature. Crossovers were located predominantly in regions of greatest intertypic homology, and we conclude that primary recombination occurred with the L segment of the genome in either orientation.