The principal hydrogen donor for the herpes simplex virus type 1-encoded ribonucleotide reductase in infected cells is a cellular thioredoxin.

In this study herpes simplex virus type 1-encoded ribonucleotide reductase was shown to be able to utilize thioredoxin purified from the cyanobacterium Anabaena variabilis as a hydrogen donor for the enzyme. An assay has been developed to search for proteins which can function as a hydrogen donor for the viral ribonucleotide reductase. A protein has been identified and purified to homogeneity from infected cell extracts by a combination of fast protein liquid chromatography and gel filtration. This protein, which is also present in mock-infected cells, has been identified as a host cell thioredoxin by similarities in its physical characteristics with other thioredoxins. No evidence for the existence of a major virus-induced thioredoxin was obtained, suggesting that the host cell thioredoxin functions as the hydrogen donor for the herpes simplex virus type 1 ribonucleotide reductase in the infected cell.