Isolation and characterization of two herpes simplex virus type 1 variants containing duplication of sequences within the unique long component of their genomes.

: This paper reports the first spontaneous isolation of two DNA duplication variants in the unique long (UL) component of herpes simplex virus type 1 (HSV-1) strain 17+ genome, one (1719) with a duplication of 7.5 kb DNA sequences centered around OriL and the other (1740In) with a 356 bp DNA duplication between the UL19 (MCP) and UL20 open reading frames (ORFs). The variant 1719 is stable with the rare isolation of a wild type (strain 17+) genome presumably generated by the excision of the duplicated sequences during homologous recombination. Because of the 7.5 kb duplication, UL29 (DBP) is diploid and UL30 (DNA pol) is present as one complete and one partial copy. Although duplication in the variant 1740In involved sequences from the UL20 ORF, the virus produces an intact UL20 gene product. Both variants show normal growth characteristics when compared with the parental viruses. DNA duplications in these variants suggest a link between replication and recombination in HSV-1.