Yeast Genetics and Molecular Biology 2000
University of Washington
Seattle, Washington USA
July 2000

Name: Raveh, Dina
Mailing Address: Life Sciences, Ben Gurion University, Henrietta Szold, Beersheba, 84105, Israel
Email Address: raveh@bgumail.bgu.ac.il
Phone & FAX numbers: 972-7-646-1371 & 972-7-647-2890

#024

Functions of the DNA damage response pathway target Ho endonuclease of yeast for degradation via the ubiquitin-26s proteasome system.
Ludmila Kaplun (1), Yelena Ivantsiv (1), Daniel Kornitzer (2), Dina Raveh (1)
(1) Life Sciences, Ben Gurion University, Henrietta Szold, Beersheba, 84105, Israel; (2) Department of Microbiology, Faculty of Medicine, Technion, Haifa, Israel

Ho endonuclease of S. cerevisiaeis a homing endonuclease that makes a site-specific double strand break in the MAT gene in late G1. We found that Ho is rapidly degraded via the ubiquitin-26S proteasome system through two ubiquitin-conjugating enzymes UBC2Rad6 and UBC3Cdc34. UBC2Rad6 is complexed with the ring finger DNA-binding protein Rad18 and we find that Ho is stabilized in rad18 mutants. The Ho degradation pathway involving UBC3Cdc34 goes through the SCF ubiquitin ligase complex and we have identified a novel F-box protein, YML088w, that is required for Ho degradation. Components of a defined pathway of the DNA damage response, MEC1, RAD9 and CHK1, are also necessary for Ho degradation, whereas functions of the RAD24 epistasis group and the downstream effector RAD53 have no role in degradation of Ho. Our results indicate a link between the double strand break induced by Ho and its destruction.

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