Top3-Rmi1 DNA Single-Strand Decatenase Is Integral to the Formation and Resolution of Meiotic Recombination Intermediates

Abstract

Summary The topoisomerase III (Top3)-Rmi1 heterodimer, which catalyzes DNA single strand passage, forms a conserved complex with the Bloom's helicase (BLM, Sgs1 in budding yeast). This complex has been proposed to regulate recombination by disassembling double-Holliday junctions in a process called dissolution. Top3-Rmi1 has been suggested to act at the end of this process, resolving hemicatenanes produced by earlier BLM/Sgs1 activity. We here show that, to the contrary, Top3-Rmi1 acts in all meiotic recombination functions previously associated with Sgs1, most notably as an early recombination intermediate chaperone, promoting regulated crossover and noncrossover recombination, and preventing aberrant recombination intermediate accumulation. In addition, we show that Top3-Rmi1 has important Sgs1-independent functions that ensure complete recombination intermediate resolution and chromosome segregation. These findings indicate that Top3-Rmi1 activity is important throughout recombination, to resolve strand crossings that would otherwise impede progression through both early steps of pathway choice and late steps of intermediate resolution.

The Nucleoporin Nup2 Contains a Meiotic-Autonomous Region that Promotes the Dynamic Chromosome Events of Meiosis

“…Disruption of the recombination program can also result in more complex forms of JMs (Oh et al 2007;Kaur et al 2015;Tang et al 2015). We found that the JM lifespan in nup2D (0.6 hr) was longer than that in WT (0.3 hr), but not to the extent of ndj1D (1.6 hr; Figure 6C).…”

“…These two phenotypes are similar to the meiotic depletion alleles of top3/rmi1 that disrupt decatenase activity and lead to the accumulation of unresolved JMs. These mutations block nuclear divisions without disrupting the meiotic program, also known as "meiotic catastrophe" (Gangloff et al 1999;Jessop and Lichten 2008;Oh et al 2008;Kaur et al 2015;Tang et al 2015). Similar to the top3/rmi1 mutants, deletion of SPO11 or mutating the catalytic residue of SPO11 (SPO11-Y135F) suppressed the nup2D ndj1D block to nuclear divisions, presumably by eliminating a physical constraint caused by intermediates, or aberrant structures, associated with meiotic recombination.…”

“…While these values could be highly skewed from the very low sporulation rate, they also lend some insight into the cause of the overall failure to form binucleate cells. For example, if segregation was blocked due to a defect in resolving doubleHolliday junctions (Kaur et al 2015;Tang et al 2015), there may be a small fraction of cells that escape this block by successfully resolving all joint molecules (JMs). Therefore, the relatively high level of viability suggests that the inability of the double mutant to form binucleate cells is not due to a catastrophic defect in repairing Spo11-induced DSBs, but instead may affect a later step such as CO resolution (see below).…”

“…Even though it appears that most of the JMs are turned over at the HIS4LEU2 hotspot, less efficient repair at other loci could impede chromosome separation. This could explain the relatively high spore viability of the nup2D ndj1D double mutant; if segregation was blocked due to a defect in resolving double-Holliday junctions (Kaur et al 2015;Tang et al 2015), there may be a small fraction of cells that escape this block by successfully resolving all JMs.…”

A Delicate Balance Between Repair and Replication Factors Regulates Recombination Between Divergent DNA Sequences inSaccharomyces cerevisiae

“…Sgs1 is known to interact with the topoisomerase complex Top3-Rmi1 in a variety of processes including 59 to 39 strand resection during homologous recombination and dissolution of double Holliday junctions (Bennett et al 2000;Fricke et al 2001;Chang et al 2005;Mullen et al 2005;Ui et al 2005;Chen and Brill 2007;Cejka and Kowalczykowski 2010;Niu et al 2010). Recently Sgs1 and Top3-Rmi1 were shown to have interdependent and independent functions in meiosis (Kaur et al 2015;Tang et al 2015). However an antirecombination role for the Top3-Rmi1 complex has not been clearly established, though previous studies showed that top3D mutants increased recombination between divergent DNA sequences (Wallis et al 1989;Bailis et al 1992).…”