Three Mutants of Herpes Simplex Virus Type 2: One Lacking the Genes US10, US11 and US12 and Two in which RS Has Been Extended by 6 kb to 0{middle dot}91 Map Units with Loss of US Sequences between 0{middle dot}94 and the US/TRS Junction

Abstract

In the process of generating restriction endonuclease site deletion mutants, we have isolated and characterized three mutants of herpes simplex virus type 2 (HSV-2), strain HG52, with large genomic deletions in US and TRS. The deleted sequences (7.5 kb) extend from 0.94 map coordinates (m.c.) to 0.99 m.c. and are presumed to contain the HSV-2 gene equivalents of US10, 11 and 12, one copy of immediate early (IE) gene 3 and one copy of an origin of replication (ORIS). One of the mutants (HG52X163X12) has a simple deletion whereas in the two others (HG52X163X14 and HG52X163X21) the deleted sequences have been replaced by inverted duplications of US/IRS sequences between 0.83 and 0.91 m.c. such that the molecules have short region inverted repeats extended by 6 kb on either side. All three are viable, stable and grow in tissue culture indicating that the polypeptides coded by the HSV-2 genes equivalent to US10, 11 and 12 are non-essential for lytic growth in BHK21/C13 cells. In addition the lack of one copy of the HSV-2 equivalent of IE gene 3 and ORIS in HG52X163X12 shows that only one copy of each suffices for viability. However the temperature restriction of the mutants at 38.5.degree. C suggests that one or more of the polypeptides coded by the deleted sequences may be required in conjunction with another polypeptide(s) for viral growth or stability at the higher temperature.