Bacteriophage‐Induced Ribonucleotide Reductase Systems

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Abstract
Infection of Escherichia coli with bacteriophage T5 caused a more than 20‐fold increase in ribonucleotide reductase activity in crude cell extracts. The phage induced the formation of a new ribonucleotide reductase and a new thioredoxin.The T5‐specific ribonucleotide reductase was defined by its ability to accept the T5‐induced thioredoxin as hydrogen donor. However, the enzyme could also accept E. coli thioredoxin as hydrogen donor and it was inhibited by antisera against subunit B2 of E. coli ribonucleotide reductase. The crude phage enzyme preparation studied preferred CTP to CDP and CMP as substrate and required magnesium and ATP for activity. Its behaviour towards allosteric effectors was different from that of the host enzyme.T5‐induced thioredoxin chromatographed together with E. coli thioredoxin on DEAE‐cellulose but could be separated from the latter by immunoadsorbent chromatography. T5 thioredoxin was reduced by E. coli thioredoxin reductase but could not serve as hydrogen donor of E. coli ribonucleotide reductase.Bacteriophage T6 induced a new ribonucleotide reductase and a new thioredoxin upon infection. The T6‐induced proteins cross‐reacted functionally and immunologically with the corresponding T4‐induced proteins.Infection of E. coli B with phage T7 or induction of the lysogens E. coli K‐39 (λ+) and E. coli W‐3350 (λc1857) caused no increase in reductase activity and chromatography of cell extracts gave no evidence for the presence of new thioredoxins.

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