| dc.description.abstract | Replication Factor A (RFA) is an essential heterotrimeric single-stranded DNA (ssDNA) binding complex, comprised of Rfa1, Rfa2, and Rfa3 in Saccharomyces cerevisiae. RFA is required for DNA replication, repair, recombination, and cell cycle regulation. RFA acts as a sensor of ssDNA, a common intermediate of these processes, and coordinates these processes through recruitment of proteins. For example, during the DNA damage response (DDR), RFA-coated ssDNA is necessary for the recruitment and activation of the sensor kinase Mec1. Additional checkpoint proteins, also recruited by RFA, are necessary for the downstream recruitment and activation of the effector kinase Rad53 that ultimately leads to cell cycle arrest. Thus, RFA acts as a bridge to recruit the proteins required for checkpoint regulation in response to DNA damage.
Importantly, cell cycle resumption is contingent on Rad53 deactivation. There are two known scenarios in which Rad53 is deactivated: (1) checkpoint recovery, in which cells resume the cell cycle after DNA repair or (2) checkpoint adaptation, in which cells proceed with the cell cycle despite the continued presence of irreparable DNA damage.
Previous work has demonstrated that cells undergoing checkpoint adaptation display late Rfa2 N-terminal (NT) phosphorylation that is correlated with the inactivation (dephosphorylation) of Rad53. Additionally, the use of rfa2 NT mutations consistently demonstrate that a negatively charged NT promotes adaptation in all adaptation-deficient strain backgrounds investigated. Interestingly, Rfa2 NT phosphorylation also occurs early during meiosis.
This work demonstrates that: (1) Rfa1-DBD-F participates in protein-protein interactions that are sensitive to DNA damage, (2) Rfa2 phosphorylation increases the DNA damage sensitivity of mutants with deficient DNA damage checkpoints, (3) the Rfa2 NT is required for proper progression through meiosis that appears to be unrelated to RFA functions in replication or DNA repair by homologous recombination (HR), and (4) Rfa2 phosphorylation may regulate Mec1 checkpoint signaling during the DDR to control checkpoint exit and cell cycle resumption. A mechanism is proposed that considers both Rfa1 DBD-F and the Rfa2 NT involvement to initiate HR repair that essentially allows for the continuation of the cell cycle by the delocalization of Mec1. | en_US |
