J. Biol. Chem., Vol. 263, Issue 13, 6193-6201, May, 1988
Defect in synthesis of deoxyribonucleotides by a bacteriophage T4 nrdB mutant is suppressed on mutation of T4 DNA topoisomerase gene
DO Wirak, KS Cook and GR Greenberg
Department of Biological Chemistry, University of Michigan, Ann Arbor 48109.
Bacteriophage T4 infection is known to induce the formation of a complex of
enzymes effecting the de novo synthesis of deoxyribonucleoside
triphosphates, which in turn are channeled into T4 DNA replication. The
first step in this pathway is catalyzed by a ribonucleoside diphosphate
reductase, comprised of subunits coded by T4 genes nrdA and nrdB. Maximum
rates of synthesis of the pyrimidine deoxyribonucleotides and of DNA
replication in vivo also require a type II DNA topoisomerase encoded by T4
genes 39, 52, and 60. We report the identification of a unique mutant,
nrdB93, and the suppression of its defective deoxyribonucleotide synthesis
by a gene 39 mutation, 39-01. After infection by 39-01, DNA synthesis and
plaque formation were temperature-sensitive, but nearly wild type rates of
deoxyribonucleotide synthesis were retained at all temperatures. The nrdB93
mutation had a profound effect on deoxyribonucleotide synthesis at 41
degrees C; even at the permissive temperature of 30 degrees C, synthesis
was reduced to 30% of that of wild type or 39-01. However, on infection at
30 degrees C by the double mutant, 39-01 nrdB93, the level of
deoxyribonucleotide synthesis again reached that of wild type phage
infections; involvement of the comparable host enzyme in the suppression
process has been excluded. Suppression of the effect of nrdB93 by 39-01
implicates the gene 39 product in the regulation of nrdB expression. The
accompanying paper (Cook, K. S., Wirak, D. O., Seasholtz, A. F., and
Greenberg, G. R. (1988) J. Biol. Chem. 263, 6202- 6208) examines the nature
of the suppression process at the molecular level.
CiteULike 
Complore 
Connotea 
Del.icio.us 
Digg 
Reddit 
Technorati What's this?
