Key words: HSV-1/XbaI site deletion~synthetic ol gonucleotide Generation of a Herpes Simplex Virus Type I Variant Devoid ofXbal Sites

Using both selection enrichment and site-directed mutagenesis, a herpes simplex virus type 1 (HSV-I) strain 17 genome lacking all four XbaI sites has been generated. The site at 0.45 map units which lies within the gene coding for a polypeptide of 28 000 molecular weight was removed by selection enrichment, while the site at 0.29 map units which lies within the gene coding for glycoprotein H was removed by site-directed mutagenesis. The parental virus from which these two XbaI sites were deleted had previously had the sites at 0-07 and 0.63 map units removed through selection enrichment. The variant devoid of XbaI sites (X4) showed normal growth characteristics; its phenotype was normal apart from the absence of the thymidine kinase protein, which is believed to be unrelated to the loss of XbaI sites. Recombination i herpes simplex virus (HSV) is poorly understood, both in terms of the role of viral and host functions (DasGupta & Summers, 1980) and of the possible ffect of particular base sequences, e.g. hot spots, on recombination frequency. The contribution of different genome isomers to the recombination process is unclear, although Honess et al. (1980) suggested a circular linkage map indicating the involvement of all four isomers. Linkage maps of severa