Conversion of a fraction of the unique sequence to part of the inverted repeats in the S component of the herpes simplex virus type 1 genome.

A novel genome variant of herpes simplex virus type 1 (HSV-1) was isolated, in the S component of which a fraction of the unique sequence (map units 0.865 to 0.880) was converted to part of the diploid inverted repeats and another fraction of the unique sequence (map units 0.937 to 0.955) had been deleted. The S component of the variant consisted of a shortened unique sequence (map units 0.880 to 0.937) and a pair of elongated inverted repeats (map units 0.820 to 0.880, and 0.937 to 1.000). The conversion occurred as a result of a recombination event between two points (map units 0.880 and 0.937) having a 5 base pair stretch (5'-CCCCG-3') of homology, in an inverted direction in the unique sequence. An involvement of the mechanism causing L-S inversion was inferred to account for the generation of the variant, as there are multiple copies of the 5'-CCCCG-3' stretch in the 'a' sequences. The occurrence of the variant indicates that the products of HSV-1 genes US9, US10, US11 and US12 are unnecessary for an HSV-1 productive infection in tissue culture cells, and also suggests the presence of a mechanism whereby expansion of the inverted repeats could occur.