Mapping of the deletion in the genome of HSV-1 strain HFEM responsible for its avirulent phenotype.

To determine the exact map position of the deletion in the genome of HSV-1 strain HFEM, the Bam HI DNA fragment B of the HSV-1 strains HFEM, F, and of HSV-R-HFehx-C19 were cloned in the Bam HI site of the bacterial plasmid vector pAT153 and analysed in detail. Analysis of the insert of the three recombinant plasmids harbouring the Bam HI DNA fragment B of HSV-1 strain F (pHSF-B-B), HSV-1 strain HFEM (pHSHF-B-B), and recombinant HSV-R-HFehx-C19 (pHSR19-B-B) was performed using a variety of restriction enzymes and Southern blot hybridization. These comparative studies revealed that the HpaI DNA fragment P of the intact viral genome of HSV-1 strain F is not present in the genome of HSV-1 strain HFEM, indicating that the deletion in HSV-1 strain HFEM corresponds to this fragment, which spans the coordinates 0.762 to 0.790 of the HSV-1 DNA. The size of the deletion was found to be 4.1 kbp, corresponding to 2.7 Md.