Isolation and Characterization of Deletion Mutants of Herpes Simplex Virus Type 2 (Strain HG52)

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Abstract
Evidence is provided that 2 variants lacking the XbaI site at map coordinate 0.7 were selected following XbaI treatment of the DNA of herpes simplex virus type 2 strain HG52. One mutant had lost the 0.7 restriction site due to a deletion of .apprx. 150 base pairs and in the other the site loss was due to a similar sized sequence insertion. Following XbaI treatment, 4 variants with deletions ranging in size from 1.5 kb (kilobase) (in both TRL and IRL) to 9 kb in IRL were isolated. Substantial deletions in the long terminal repeat regions of HG52 are present with a frequency of 24% of genomes in the elite stock, a variant with a 3.75 kb deletion in IRL making up 10% and 1 with a 1.5 kb deletion in both IRL and TRL making up 14%. Two variants isolated after X4baI treatment of viral DNA were identical to the deletion prototype within the elite stock, suggesting that these variants were not generated as a result of XbaI treatment but pre-existed in the viral DNA pool. The deletion variants were stably maintained during routine stock propagation, were viable and could be propagated as cloned populations. The deletions did not have a marked deleterious effect on the 2-step growth kinetics of the virus.