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Yeast Rad17/Mec3/Ddc1: A Sliding Clamp for the DNA Damage Checkpoint

Jerzy Majka and Peter M. J. Burgers
Proceedings of the National Academy of Sciences of the United States of America
Vol. 100, No. 5 (Mar. 4, 2003), pp. 2249-2254
Stable URL: http://www.jstor.org/stable/3139513
Page Count: 6
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Yeast Rad17/Mec3/Ddc1: A Sliding Clamp for the DNA Damage Checkpoint
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Abstract

The Saccharomyces cerevisiae Rad24 and Rad17 checkpoint proteins are part of an early response to DNA damage in a signal transduction pathway leading to cell cycle arrest. Rad24 interacts with the four small subunits of replication factor C (RFC) to form the RFC-Rad24 complex. Rad17 forms a complex with Mec3 and Ddcl (Rad17/3/1) and shows structural similarities with the replication clamp PCNA. This parallelism with a clamp-clamp loader system that functions in DNA replication has led to the hypothesis that a similar clamp-clamp loader relationship exists for the DNA damage response system. We have purified the putative checkpoint clamp loader RFC-Rad24 and the putative clamp Rad17/3/1 from a yeast overexpression system. Here, we provide experimental evidence that, indeed, the RFC-Rad24 clamp loader loads the Rad17/3/1 clamp around partial duplex DNA in an ATP-dependent process. Furthermore, upon ATP hydrolysis, the Rad17/3/1 clamp is released from the clamp loader and can slide across more than 1 kb of duplex DNA, a process which may be well suited for a search for damage. Rad17/3/1 showed no detectable exonuclease activity.

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