Replication Characteristics of Herpes Simplex Virus Type-1 (HSV-1) Recombinants in 3 Types of Tissue Cultures

A complication in the analysis of the role of ICP34.5 gene in the herpes simplex virus type-1 (HSV-1) lifecycle is the presence of overlapping antisense gene, open reading frame P (ORF P), which is also deleted in HSV-1 ICP34.5 negative mutants. A HSV-1 wild type strain (17+) ICP34.5/ORF P deletion mutant (1716) is totally avirulent in animal models and impaired in a number of in vitro functions: replication in 3T6 cells and replication and shutoff of cellular protein synthesis in SK-N-SH cells. To attribute characteristics of 1716 to each of these two genes (ICP34.5 or ORF P), a number of HSV-1 recombinant viruses that express ICP34.5 and ORF P independently were constructed, purified and characterized. The parent of these recombinants is 1716 and they are (so called): 1622, expressing ICP34.5 1624/24.5, expressing ORF P and 1625, expressing both ICP34.5 and ORF P in separate loci. Using homologous recombination in cell culture, the recombinants were constructed and their DNA were analyzed by Southern-blotting. Expression of ICP34.5 and ORF P from the recombinants was checked by Western-blotting. Using cell culture, titration and plaque assay techniques, replication kinetics of the recombinants were compared with 17+ and 1716 in 3 cell lines, BHK, 3T6, and SK-N-SH. The results showed that (i) ICP34.5 restored the ability to replicate and prevent host shutoff similar to wild type in SK-N-SH cells (ii) ICP34.5 restored the replication phenotype to near wild type levels in 3T6 cells and (iii) ORF P expression had no effect on the replication of these mutants. The characteristics of 1716 is obviously due to the lack of ICP34.5 and ORF P has no role in the characteristics studied. Thus, the function of ORF P still has to be determined.