Complete genome duplication requires a close collaboration between the replication machinery and many regulatory factors. These factors can assist replisomes in coping with large numbers of template obstacles, and their defects are frequently associated with human diseases such as cancer and DNA damage syndromes. It is our long-term goal to understand how replication regulatory proteins interact with the replisome and aid replication. We and others have shown that the evolutionarily conserved Smc5/6 complex is essential for promoting replication under normal and DNA damaging conditions. During the last two cycles of this grant, we have made significant progress in elucidating the structure of this complex, its unique SUMO E3 activity, and its multiple effects on genome maintenance in the budding yeast model system. Importantly and most relevant to the current proposal, we recently showed that Smc5/6 and its binding partner, the scaffold protein Rtt107, comprise a new pathway that aids large replicon synthesis. Large replicons are difficult to duplicate and strongly associated with fragile sites and other forms of genomic instability. Investigating the mechanisms by which Smc5/6 and Rtt107 facilitate large replicon synthesis will broaden our understanding of the maintenance of high-risk genomic regions. We found that Smc5/6 and Rtt107 interact with DNA polymerase and helicase complexes and contribute to their sumoylation. Moreover, these sumoylation events influence replication. Based on these findings, we hypothesize that Smc5/6 and Rtt107 directly promote replisome function to aid large replicon synthesis. Extending from this work, we showed that Rtt107 is the hub of a protein network composed of Smc5/6 and other genome maintenance factors. How Rtt107 supports the interactions within this network and how each interaction contributes to replication are important questions to address. In the next funding cycle, we propose to test our hypothesis stated above by examining how Smc5/6 and Rtt107 affect replication fork functions during large replicon synthesis, and define the biochemical features of the Smc5/6 and Rtt107 interactions with DNA polymerase and helicase complexes. In addition, we will determine how the sumoylation of DNA polymerase and helicase complexes affects the initiation and elongation stages of replication. Findings from these studies will shed light on the roles of Smc5/6, Rtt107, and SUMO in promoting the completion of large replicon synthesis. Finally, we will investigate the biochemical basis of Rtt107-mediated interactions and the functions of each interaction. To achieve these goals, we will use a combination of genetic, biochemical, biophysical approaches in the highly effective yeast system. Outcomes of the proposed work will expand our view on how large replicon synthesis is achieved, how SUMO regulates replication, and how the Rtt107 interactome contributes to genome duplication. As such, these studies will have broad implications in our understanding of genome maintenance mechanisms.

Public Health Relevance

Genome duplication has to be accurate in order to prevent DNA errors that can lead to many forms of diseases. A close collaboration between the DNA replication machineries and many regulatory factors is critical for accomplishing this task. This project will use a combination of approaches to understand how exactly the regulatory proteins can help faithful DNA replication.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
Research Project (R01)
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Molecular Genetics A Study Section (MGA)
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Reddy, Michael K
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Sloan-Kettering Institute for Cancer Research
New York
United States
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Zhao, Xiaolan (2018) SUMO-Mediated Regulation of Nuclear Functions and Signaling Processes. Mol Cell 71:409-418
Peng, Xiao P; Lim, Shelly; Li, Shibai et al. (2018) Acute Smc5/6 depletion reveals its primary role in rDNA replication by restraining recombination at fork pausing sites. PLoS Genet 14:e1007129
Dhingra, Nalini; Zhao, Xiaolan (2017) A guide for targeted SUMO removal. Genes Dev 31:719-720
Meng, Xiangzhou; Zhao, Xiaolan (2017) Replication fork regression and its regulation. FEMS Yeast Res 17:
Wei, Lei; Zhao, Xiaolan (2016) A new MCM modification cycle regulates DNA replication initiation. Nat Struct Mol Biol 23:209-16
Silva, Sonia; Altmannova, Veronika; Eckert-Boulet, Nadine et al. (2016) SUMOylation of Rad52-Rad59 synergistically change the outcome of mitotic recombination. DNA Repair (Amst) 42:11-25
Bonner, Jaclyn N; Choi, Koyi; Xue, Xiaoyu et al. (2016) Smc5/6 Mediated Sumoylation of the Sgs1-Top3-Rmi1 Complex Promotes Removal of Recombination Intermediates. Cell Rep 16:368-378
Hang, Lisa; Zhao, Xiaolan (2016) The Rtt107 BRCT scaffold and its partner modification enzymes collaborate to promote replication. Nucleus 7:346-51
Dummer, Antoinette M; Su, Zhangli; Cherney, Rachel et al. (2016) Binding of the Fkh1 Forkhead Associated Domain to a Phosphopeptide within the Mph1 DNA Helicase Regulates Mating-Type Switching in Budding Yeast. PLoS Genet 12:e1006094
Bonner, Jaclyn N; Zhao, Xiaolan (2016) Replication-Associated Recombinational Repair: Lessons from Budding Yeast. Genes (Basel) 7:

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