J. Biol. Chem., Vol. 255, Issue 16, 7583-7588, Aug, 1980
T4 ribonucleotide reductase. Physical and kinetic linkage to other enzymes of deoxyribonucleotide biosynthesis
JR Allen, GP Reddy, GW Lasser and CK Mathews
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.
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