The loss of the cleavage site between BamHI-T and BamHI-J' fragments of herpes simplex virus type 1 (HSV-1) genome shown in one of the seven substrains of the Miyama strain

The profiles of DNA fragments, generated by a restriction endonuclease BamHI, in the unique regions of herpes simplex virus type 1 (HSV-1) were compared among seven substrains originally derived from the parental Miyama strain. These substrains consist of five CPE variants (-GCr, -GCf, +GC (LPV), +GC (SPV) and +GC (81)) and two descendent strains of -GCr (αV and βV), both recovered from persistently infected L cell cultures originally established with -GCr. Some heterogeneous fragments were recognized among the seven substrains. The Southern blot hybridization analysis, using the subcloned DNA fragments of -GCr as probes, revealed the loss of the cleavage site between BamHI-T and BamHI-J' fragments in one of these substrains, αV. In vitro viral reproduction in an enormous number of cycles, which took place for a long period of 14 years in a persistently infected culture, might cause occasional spontaneous mutations of the virus carried in this culture and result in the loss of the cleavage site in the unique region of its genome.