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Mol. Cell. Biol., 05 1997, 2381-2390, Vol 17, No. 5
AE Parker, RK Clyne, AM Carr and TJ Kelly
Replication protein A (RPA) is a heterotrimeric single-stranded DNA-
binding protein present in all eukaryotes. In vitro studies have implicated
RPA in simian virus 40 DNA synthesis and nucleotide excision repair, but
little direct information is available about the in vivo roles of the
protein. We report here the cloning of the largest subunit of RPA (rpa1+)
from the fission yeast Schizosaccharomyces pombe. The rpa1+ gene is
essential for viability and is expressed specifically at S phase of the
cell cycle. Genetic analysis revealed that rpa1+ is the locus of the S.
pombe radiation-sensitive mutation rad11. The rad11 allele exhibits
pleiotropic effects consistent with an in vivo role for RPA in both DNA
repair and DNA synthesis. The mutant is sensitive to both UV and ionizing
radiation but is not defective in the DNA damage- dependent checkpoint,
consistent with the hypothesis that RPA is part of the enzymatic machinery
of DNA repair. When incubated in hydroxyurea, rad11 cells initially arrest
with a 1C DNA content but then lose viability coincident with reentry into
S phase, suggesting that DNA synthesis is aberrant under these conditions.
A significant fraction of the mutant cells subsequently undergo
inappropriate mitosis in the presence of hydroxyurea, indicating that RPA
also plays a role in the checkpoint mechanism that monitors the completion
of S phase. We propose that RPA is required to maintain the integrity of
replication complexes when DNA replication is blocked. We further suggest
that the rad11 mutation leads to the premature breakdown of such complexes,
thereby preventing recovery from the hydroxyurea arrest and eliminating a
signal recognized by the S-phase checkpoint mechanism.
Copyright © 1997, American Society for Microbiology
The Schizosaccharomyces pombe rad11+ gene encodes the large subunit of replication protein A
Department of Molecular Biology and Genetics, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.
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