The integrity of the genome is continuously challenged from both endogenous and exogenous sources. In order to maintain genomic stability, the cell has acquired sophisticated surveillance mechanisms of genome integrity. One of these mechanisms is the DNA damage checkpoint, which detects DNA lesions and initiates appropriate cellular responses, including cell cycle arrest and DNA repair. Another essential aspect in preserving genome integrity is the accurate chromosome distribution between daughter cells at cell division. This is mainly achieved due to activities of the spindle assembly checkpoint (SAC), which responds to unattached kinetochores or lack of tension between sister chromatids and arrests the cell cycle until all chromosomes are properly attached to the spindle. However, if the trigger activating either the DNA damage checkpoint or the SAC persists, then cell cycle arrest will not necessary be maintained indefinitely, because the cell can re-enter the cell cycle through a process termed adaptation.
In this study, I investigated the role of the Saccharomyces cerevisiae Rdh54 DNA translocase at kinetochores. Rdh54 is involved in DNA repair by homologous recombination (HR) and is required for adaptation to the DNA damage checkpoint. At the cell biological level, fluorescently tagged Rdh54 localizes not only to DNA repair sites but also to kinetochores. To understand the functional importance of Rdh54 localization to kinetochores, I screened for potential interaction partners of Rdh54 at the kinetochore using bimolecular fluorescence complementation (BiFC) and found that Rdh54 shows extensive interactions with the outer kinetochore. Furthermore, I showed that cells lacking Rdh54 function are deficient in resuming cell cycle progression in the presence of benomyl, an agent that depolymerizes microtubules, thereby inducing the SAC. Based on these and other data, I proposed a model, where Rdh54 promotes adaptation not only to the DNA damage checkpoint but also to the SAC by competing with SAC proteins for binding sites at the kinetochore in late metaphase, thus reducing SAC signaling and facilitating the escape from cell cycle arrest mediated by the SAC. Further analysis will test this model experimentally.