IDENTIFICATION OF A 2ND FUNCTIONAL GLUTAREDOXIN ENCODED BY THE BACTERIOPHAGE-T4 GENOME

Thioredoxins and glutaredoxins are small ubiquitous redox proteins tha t were discovered as hydrogen donors for ribonucleotide reductase, the key enzyme for deoxyribonucleotide biosynthesis. Some organisms encod e more than one redox protein. In this study, we demonstrate that an o pen reading frame in the bacteriophage T4 genome, reported earlier and designated as Y55.7 (Tomaschewski, J., and Ruger, W. (1987) Nucleic A cids Res. 15, 3632-3633), encodes a second functional redox protein. G ene y55.7 was cloned and expressed in Escherichia coli. Purified Y55.7 protein had glutathione-dependent thioltransferase and dehydroascorba te reductase activities indicative of a functional glutaredoxin. The p rotein is expressed at all stages of the T4 infection cycle and can se rve as a hydrogen donor for the phage ribonucleotide reductase in in v itro experiments.