Abstract:
Deoxyribonucleotide pools are maintained at levels that support efficient and yet accurate DNA replication and repair. Rad53 is part
of a protein kinase regulatory cascade that, conceptually, promotes dNTP accumulation in four ways: (1) it activates the transcription of
ribonucleotide reductase subunits by inhibiting the Crt1 repressor; (2) it plays a role in relocalization of ribonucleotide reductase subunits
RNR2 and RNR4 from nucleus to cytoplasm; (3) it antagonizes the action of Sml1, a protein that binds and inhibits ribonucleotide
reductase; and (4) it blocks cell-cycle progression in response to DNA damage, thus preventing dNTP consumption through replication
forks. Although several lines of evidence support the above modes of Rad53 action, an effect of a rad53 mutation on dNTP levels has not
been directly demonstrated. In fact, in a previous study, a rad53-11 mutation did not result in lower dNTP levels in asynchronous cells or
in synchronized cells that entered the S-phase in the presence of the RNR inhibitor hydroxyurea. These anomalies prompted us to investigate
whether the rad53-11 mutation affected dNTP levels in cells exposed to a DNA-damaging dose of ethylmethyl sulfonate (EMS).
Although dNTP levels increased by 2- to 3-fold in EMS treated wild-type cells, rad53-11 cells showed no such change. Thus, the results
indicate that Rad53 checkpoint function is not required for dNTP pool maintenance in normally growing cells, but is required for dNTP
pool expansion in cells exposed to DNA-damaging agents.
2006 Elsevier Inc. All rights reserved.
