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

SUMMARYin 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 (ORls). One of the mutants (HG52X163X12) has a simple deletion whereas in the two others (HG52X 163X14 and HG52X163X21) the deleted sequences have been replaced by inverted duplications of Us/IRs sequences between 0.83 and 0-91 m.c. such that the molecules have short region inverted repeats extended by 6 kb on either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 n0n-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 °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. INTRODUCTIONDeletions in one copy of the long repeat sequences of herpes simplex virus type 2 (HSV-2) strain HG52 occur at a frequency of 24~o by passage eight from the original field isolation (Harland & Brown, 1985). The described deletions range in size with the maximum being 9 kb and encompass the entire long repeat with the exception of the 'a' sequences. Other strains of HSV-2 exhibit simdar deletions showing that the HG52 strain is not exceptional. Deletions in the long repeat had been observed previously in intertypic reeombinants when Davison et al. (1981) suggested that they probably arose as a consequence of heterotypic repetitive regions. Our observations show that this could not be the explanation but that deletions within one copy of the long repeats of the HG52 genome are relatively common. These deletion variants do not have a selective disadvantage (Harland & Brown, 1985); thus only one copy of immediate early (IE) gene 1 and the other coding information within the long repeats is sufficient for viable growth in tissue culture. The product of IE gene 1, i.e. Vm,~ IE 110, in conjunction with V mw IE175 has an enhancing effect on early polypeptide transcription (Everett, 1984) but it has not been shown whether V~wlE110 is essential for lytic growth.The high frequency of spontaneous deletions within the long repetitive sequences raises the question of whether similar deletions could occur in the short repetitive sequences of the genome. The repeat (TRs) and unique short (Us) regions of the HSV-l genome have been fully sequenced (Murchie & McGeoch, 1982;McGeoch et al., 1985), The IE3 gene coding for

Herpes simplex virus type 1 deletion variants 1714 and 1716 pinpoint neurovirulence-related sequences in Glasgow strain 17+ between immediate early gene 1 and the 'a' sequence

“…The opportunity of defining precise regions of the herpes simplex virus (HSV) genome involved in pathogenicity has been provided by the isolation of deletion variants of both HSV-1 and -2 (Brown et al, 1984;Harland & Brown, 1985Brown & Harland 1987;MacLean & Brown, 1987a, b;Efstathiou et al, 1989). We have recently shown that the JH2604 deletion variant of HSV-2 strain HG52 (Harland & Brown, 1985) is avirulent when inoculated intracerebrally into mice, with an LDso value of > 107 p.f.u./mouse compared to < 102 p.f.u./ mouse for the parental virus (Taha et al, 1989a).…”

The Herpes Simplex Virus Type 2 (HG52) Variant JH2604 Has a 1488 bp Deletion which Eliminates Neurovirulence in Mice

“…Using HG52 as a standard, the virulence of deletion variants of HG52 (Harland & Brown, t985;Brown & Harland, 1987) is under study. One of the variants, JH2604, with a 1.5 kb deletion within each copy of the long repeat region (RL) from 0 to 0"02 and 0.81 to 0.83 map units (m.u.)…”

The JH2604 deletion variant of herpes simplex virus type 2 (HG52) fails to produce necrotizing encephalitis following intracranial inoculation of mice

“…A series of deletion variants of both HSV types 1 and 2 isolated in our laboratory provides the unique opportunity of exploring the roles of the deleted genes in the pathogenesis of the disease (Brown et al, 1984;Harland & Brown, 1985, 1989Brown & Harland, 1987;MacLean & Brown, 1987 a, b). One such variant (JH2604) of HSV-2 strain HG52 (Harland & Brown, 1985) has been shown to be completely avirulent following intracranial inoculation of mice with a LD50 of > 107 p.f.u./mouse compared to < 102 p.f.u./mouse for its parental wild-type (wt) virus (Taha et al, 1989a).…”