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Journal of Biochemistry Advance Access published online on June 23, 2006
Journal of Biochemistry, doi:10.1093/jb/mvj130
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© 2006 The Japanese Biochemical Society.
Received May 6, 2006
Accepted May 21, 2006

Regular Paper

Accumulation of FFA-1, the Xenopus Homolog of Werner Helicase, and DNA Polymerase {delta} on Chromatin in Response to Replication Fork Arrest

Noriko Sasakawa 1, Tomoyuki Fukui 1, and Shou Waga 2 *

1 Department of Biology, Graduate School of Science, Osaka University, Toyonaka, Osaka, 560-0043, Japan; Research Institute for Microbial Diseases, Graduate School of Frontier Biosciences, Osaka University, Suita, Osaka 565-0871, Japan; present address: Center for Developmental Biology, RIKEN, Kobe, Japan
2 Research Institute for Microbial Diseases, Graduate School of Frontier Biosciences, Osaka University, Suita, Osaka 565-0871, Japan; Laboratories for Biomolecular Network, Graduate School of Frontier Biosciences, Osaka University, Suita, Osaka 565-0871, Japan

* To whom correspondence should be addressed.
Shou Waga, E-mail: swaga{at}fbs.osaka-u.ac.jp


  Abstract

Werner syndrome is a genetic disorder characterized by premature aging and cancer-prone symptoms, and is caused by mutation of the WRN gene. WRN is a member of the RecQ helicase family and is thought to function in processes implicated in DNA replication and repair to maintain genome stability; however, its precise function is still unclear. We found that replication fork arrest markedly enhances chromatin binding of focus-forming activity 1 (FFA-1), a Xenopus WRN homolog, in Xenopus egg extracts. In addition to FFA-1, DNA polymerase {delta} (Pol{delta}) and replication protein A, but not DNA polymerase {varepsilon} and proliferating cell nuclear antigen, accumulated increasingly on replication-arrested chromatin. Elevated accumulation of these proteins was dependent on formation of pre-replicative complexes (pre-RCs). Double-strand break (DSB) formation also enhanced chromatin binding of FFA-1, but not Pol{delta}, independently of pre-RC formation. In contrast to FFA-1, chromatin binding of Xenopus Bloom syndrome helicase (xBLM) only slightly increased after replication arrest or DSB formation. Thus, WRN-specific, distinct processes can be reproduced in the in vitro system in egg extracts, and this system is useful for biochemical analysis of WRN functions during DNA metabolism.

Keywords: DNA polymerase {delta}; FFA-1; replication fork arrest; Werner helicase; Xenopus egg extract.
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