T4 ribonucleotide reductase. Physical and kinetic linkage to other enzymes of deoxyribonucleotide biosynthesis.

Abstract This laboratory has described a multienzyme aggregate from T4 phage-infected Escherichia coli which seems to participate in deoxyribonucleotide biosynthesis and efficient delivery of DNA precursors to the replication apparatus. This paper describes improved methodology for isolation of this aggregate, and we present three lines of evidence supporting a role for ribonucleoside diphosphate reductase in functioning of the presumed complex. 1) Ribonucleoside diphosphates are readily incorporated into DNA as deoxyribonucleotides in an in situ DNA-synthesizing system from T4 phage-infected cells. 2)Ribonucleotide reductase is associated with the complex, as shown by co-sedimentation of reductase activity with other activities in the multienzyme aggregate we have described. 3)Ribonucleotide reductase is kinetically coupled to at least four other enzymes involved in a sequential pathway. The aggregated enzymes catalyze the five-step conversion of uridine diphosphate to deoxythymidine triphosphate with but a brief lag before dTTP production reaches its maximal rate. These studies have also confirmed the existence of dCTPase-dUTPase and dCMP deaminase activities in the putative complex.