Identification of a Second Functional Glutaredoxin Encoded by the Bacteriophage T4 Genome

Thioredoxins and glutaredoxins are small ubiquitous redox proteins that were discovered as hydrogen donors for ribonucleotide reductase, the key enzyme for deoxyribonucleotide biosynthesis. Some organisms encode more than one redox protein. In this study, we demonstrate that an open reading frame in the bacteriophage T4 genome, reported earlier and designated as Y55.7 (Tomaschewski, J., and Rüger, W. (1987) Nucleic Acids Res. 15, 3632-3633), encodes a second functional redox protein. Gene y55.7 was cloned and expressed in Escherichia coli. Purified Y55.7 protein had glutathione-dependent thioltransferase and dehydroascorbate reductase activities indicative of a functional glutaredoxin. The protein is expressed at all stages of the T4 infection cycle and can serve as a hydrogen donor for the phage ribonucleotide reductase in in vitro experiments.