Rtt107 Is a Multi-functional Scaffold Supporting Replication Progression with Partner SUMO and Ubiquitin Ligases

Abstract

Summary Elucidating the individual and collaborative functions of genome maintenance factors is critical for understanding how genome duplication is achieved. Here we investigate a conserved scaffold in budding yeast, Rtt107, and its three partners: a SUMO E3 complex, a ubiquitin E3 complex, and Slx4. Biochemical and genetic findings show that Rtt107 interacts separately with these partners and contributes to their individual functions, including a role in replisome sumoylation. We also provide evidence that Rtt107 associates with replisome components, and both itself and its associated E3s are important for replicating regions far from initiation sites. Corroborating these results, replication defects due to Rtt107 loss and genotoxic sensitivities in mutants of Rtt107 and its associated E3s are rescued by increasing replication initiation events through mutating two master repressors of late origins, Mrc1 and Mec1. These findings suggest that Rtt107 functions as a multi-functional platform to support replication progression with its partner E3 enzymes.

Multi-BRCT scaffolds use distinct strategies to support genome maintenance

“…91,[109][110][111] Our recent findings suggest that when cells are under replication stress, Rtt107 and the Rtt101 complex favor the synthesis of large replicons or regions far from fired origins that occurs in the late stages of S phase. 75 This conclusion is consistent with a Xenopus study that implicates PTIP (or Swift) in later stages of replication. 67 Another study implicates the Rtt101 complex in regulating recombinational repair during replication stress.…”

“…[56][57][58]74 Unlike Dpb11, which simultaneously interacts with 2 partners using its 2 tBRCT domains, Rtt107 forms different complexes with its partners. 75 Currently it is unclear how Rtt107 achieves such binding exclusivity and what the biological consequences of this mode of interaction are. However recent studies suggest that Rtt107, in collaboration with its partners, serves as a replication accessory protein that influences DNA repair, replisome progression and checkpoint signaling.…”

“…However recent studies suggest that Rtt107, in collaboration with its partners, serves as a replication accessory protein that influences DNA repair, replisome progression and checkpoint signaling. 56,57,[75][76][77] In these capacities, these proteins are critical for genome stability, and studies of their functions have provided important insights into how replication accessory proteins facilitate genome duplication. The remaining sections describe new developments regarding Rtt107 and its partners.…”

“…91,92 Mms22 interacts with Rtt107 directly and this interaction requires the region of Rtt107 encompassing its N-terminal BRCTs. 75,91,92 Several lines of evidence suggest that the Rtt101 complex facilitates histone H3 modification and nucleosome assembly. During replication, newly synthesized histone H3, in complex with H4 and the histone chaperone Asf1, is acetylated at lysine 56 (H3K56ac) by Rtt109.…”

“…The suppression could be due to the combined effects of increasing recombination and reducing large replicons. 75,112 It is likely that Rtt107, in association with the Rtt101 E3 complex, promotes replisome progression and recombinational repair at stalled replication forks, ultimately contributing to replication recovery and large replicon synthesis. Future studies will be required to test these models and examine the molecular mechanisms by which H3 modification and chromatin assembly influence these processes.…”