Isolation and characterization of deletion mutants of herpes simplex virus type 2 (strain HG52).

We provide evidence that: (i) two variants lacking the XbaI site at map coordinate 0.7 have been selected following XbaI treatment of the DNA of herpes simplex virus type 2 strain HG52; (ii) one of these mutants had lost the 0.7 restriction site due to a deletion of approximately 150 base pairs and in the other the site loss was due to a similar sized sequence insertion; (iii) following XbaI treatment, four variants with deletions ranging in size from 1.5 kb (in both TRL and IRL) to 9 kb in IRL were isolated; (iv) 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 one with a 1.5 kb deletion in both IRL and TRL making up 14%; (v) two of the variants isolated after XbaI 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; (vi) the deletion variants were stably maintained during routine stock propagation, were viable and could be propagated as cloned populations; (vii) the deletions did not have a marked deleterious effect on the one-step growth kinetics of the virus.