REPAIR OF PSORALEN-TREATED DNA BY GENETIC-RECOMBINATION IN HUMAN-CELLS INFECTED WITH HERPES-SIMPLEX VIRUS

Abstract

Herpes simplex virus (HSV) type 1 was treated with 4,5'',8-trimethylpsoralen (psoralen) plus near-UV light to produce lesions (monoadducts and DNA cross-links) in the viral DNA. Human fibroblasts were infected by damaged virus under conditions in which either a single virus particle or several particles entered a given cell and the fraction of virus-producing cells was determined. This fraction was significantly greater for multiply infected cells than for singly infected cells, indicating that the psoralen lesions are repaired more efficiently in the presence of homologous, damaged DNA (multiplicity reactivation). Evidence is presented that HSV may code for functions which participate in its own repair, both during multiplicity reactivation and during repair which occurs in singly infected cells. Host cells deficient in repair of lesions induced by psoralen (xeroderma pigmentosum) or the DNA cross-linking agent mitomycin C (Fanconi''s anemia) exhibited normal levels of multiplicity reactivation of psoralen-treated HSV. Xeroderma pigmentosum cells, previously shown to be deficient in repair of psoralen-treated adenovirus under conditions of single infection, repaired psoralen-treated HSV at near normal levels. Recombination levels between genetically marked pairs of HSV increased after treatment of the parental viruses with psoralen, suggesting that psoralen damage stimulates genetic recombination. This stimulation provides convincing evidence for a repair pathway in which genetic recombination between damaged viral genomes can lead to the production of viable virus.