Multifunctional Roles of Saccharomyces cerevisiae Srs2 protein in Replication, Recombination and Repair

Abstract

One sentence summary: Srs2 is a multifunctional protein that acts during cell replication to insure faithful and accurate copying of genetic information. Editor: Uffe Mortensen ABSTRACTThe Saccharomyces cerevisiae Srs2 DNA helicase has important roles in DNA replication, recombination and repair. In replication, Srs2 aids in repair of gaps by repair synthesis by preventing gaps from being used to initiate recombination. This is considered to be an anti-recombination role. In recombination, Srs2 plays both prorecombination and anti-recombination roles to promote the synthesis-dependent strand annealing recombination pathway and to inhibit gaps from initiating homologous recombination. In repair, the Srs2 helicase actively promotes gap repair through an interaction with the Exo1 nuclease to enlarge a gap for repair and to prevent Rad51 protein from accumulating on single-stranded DNA. Finally, Srs2 helicase can unwind hairpin-forming repeat sequences to promote replication and prevent repeat instability. The Srs2 activities can be controlled by phosphorylation, SUMO modification and interaction with key partners at DNA damage or lesions sites, which include PCNA and Rad51. These interactions can also limit DNA polymerase function during recombinational repair independent of the Srs2 translocase or helicase activity, further highlighting the importance of the Srs2 protein in regulating recombination. Here we review the myriad roles of Srs2 that have been documented in genome maintenance and distinguish between the translocase, helicase and additional functions of the Srs2 protein.

Dissociation of Rad51 Presynaptic Complexes and Heteroduplex DNA Joints by Tandem Assemblies of Srs2

“…S. cerevisiae Srs2 contains a core SF1 helicase domain that is homologous to the bacterial helicase UvrD, a C-terminal region responsible for interactions with Rad51, and a second C-terminal domain that mediates protein-protein interactions and is a target for post-translational modifications (Figure S1A)(Niu and Klein, 2016; Sasanuma et al, 2013). For our experiments, we used Srs2 preparations that were either unlabeled, or tagged at the N-terminus with either GFP or mCherry, as indicated.…”

“…While it is established that Srs2 dismantles Rad51 filaments, it has remained unclear how Srs2 is recruited to the presynaptic complex and other HR intermediates (Antony et al, 2009; Krejci et al, 2003; Marini and Krejci, 2010; Niu and Klein, 2016; Qiu et al, 2013; Sasanuma et al, 2013; Vasianovich et al, 2017; Veaute et al, 2003). In this study, we provide evidence that Srs2 is preferentially recruited to small clusters of RPA that remain embedded within the Rad51 presynaptic complex.…”

“…Highlighting the importance of these enzymes, mutations in human HR helicases that regular HR result in diseases such as Rothmund-Thompson syndrome and Fanconi Anemia, which are characterized by genome instability and increased incidence of cancer (Brosh, 2013). Srs2 is considered a proto-typical antirecombinase due to its well-characterized ability to remove Rad51 from ssDNA (Antony et al, 2009; Krejci et al, 2003; Marini and Krejci, 2010; Niu and Klein, 2016; Qiu et al, 2013; Sasanuma et al, 2013; Vasianovich et al, 2017; Veaute et al, 2003). Deletion of the SRS2 gene results in an increase in recombination frequency, and its importance is further revealed in Δsrs2 Δsgs1 and Δsrs2 ΔRad54 double mutants, which have a synthetic lethal phenotype due the accumulation of toxic recombination intermediates (Ira et al, 2003; Klein, 2001).…”

“…Deletion of the SRS2 gene results in an increase in recombination frequency, and its importance is further revealed in Δsrs2 Δsgs1 and Δsrs2 ΔRad54 double mutants, which have a synthetic lethal phenotype due the accumulation of toxic recombination intermediates (Ira et al, 2003; Klein, 2001). Srs2 is homologous to the bacterial UvrD, PcrA and Rep helicases (Marini and Krejci, 2010; Niu and Klein, 2016). Human homologues of Srs2 have yet to be identified, although mammalian FBH1 is a potential candidate, and FBH1 can also remove Rad51 from ssDNA (Simandlova et al, 2013).…”

DNA Damage Tolerance Pathway Choice Through Uls1 Modulation of Srs2 SUMOylation in Saccharomyces cerevisiae

“…Srs2 promotes their repair by SDSA, yielding noncrossing over (non-CO) products and thus limiting loss of heterozygosity events in mitotic cells (Ira et al 2003;Niu and Klein 2016). Nonetheless, D-loops formed after Rad51 recombinasedependent strand invasion might be stabilized and extended until a second end of a DNA break is captured.…”