Generating Crossovers by Resolution of Nicked Holliday Junctions

Abstract

The double Holliday junction (dHJ) is generally regarded to be a key intermediate of meiotic recombination, whose resolution is critical for the formation of crossover recombinants. In fission yeast, the Mus81-Eme1 endonuclease has been implicated in resolving dHJs. Consistent with this role, we show that Mus81-Eme1 is required for generating meiotic crossovers. However, purified Mus81-Eme1 prefers to cleave junctions that mimic those formed during the transition from double-strand break to dHJ. Crucially, these junctions are cleaved by Mus81-Eme1 in precisely the right orientation to guarantee the formation of a crossover every time. These data demonstrate how crossovers could arise without forming or resolving dHJs using an enzyme that is widely conserved amongst eukaryotes.

The MUS81 endonuclease is essential for telomerase negative cell proliferation

“…Recent studies have indicated that these structures are possible in vivo substrates of MUS81. [30][31][32] Our results show that cleavage of telomere recombination substrates by MUS81 may be necessary for ALT cells survival, directly linking MUS81 endonuclease activity with abnormal telomere recombination in ALT cells. In addition, we present evidence indicating that telomere maintenance in the ALT pathway is a post-replicative recombination process, which is essential for ALT cell survival.…”

Genetic evidence for a role of Saccharomyces cerevisiae Mph1 in recombinational DNA repair under replicative stress

“…The 3 end invades the sister chromatid to form a Dloop ( Figure 6B) and two resolutions are plausible. (a) Mph1 processes the D-loop creating a substrate for the endonuclease Mms4/Mus81 ( Figure 6C), shown to cleave three branched DNA structures (Kaliraman et al, 2001, Osman et al, 2003. We propose that Mph1 stimulates the endonuclease Mms4/Mus81, since we found an epistatic relationship of mms4 and mus81 to mph1 in terms of sensitivity to camptothecin.…”

Mammalian BTBD12/SLX4 Assembles A Holliday Junction Resolvase and Is Required for DNA Repair

“…Nicked HJs are clipped 2-5 and 3-6 nucleotides 5' of the branch point by S. pombe and S. cerevisiae Mus81 complexes, respectively (Osman et al, 2003;Gaillard et al, 2003). In contrast, S.cerevisiae Slx1p-Slx4p (purified from bacteria) or S. pombe Slx1-Slx4 purified from endogenous sources cleaves migrating HJs in the 3' side of the homologous core Coulon et al, 2004).…”

“…As this is a critical transition, the identity of resolvase enzymes has been a central focus of the field. While MUS81-EME1 (and its yeast ortholog Mus81p-Mms4p) and Slx1p-Slx4p display a preference for flap structures and replication forks, they have also been shown to display activity towards migrating or nicked HJs, albeit in a largely non-symmetrical manner Ciccia et al, 2003;Constantinou et al, 2002;Fricke and Brill, 2003;Osman et al, 2003;Chen et al, 2001;Gaillard et al, 2003;Taylor and McGowan, 2008;Coulon et al, 2004) and Mus81 mutants are defective in resolution of cruciform structures formed by palindromic sequences that mimic a HJ in vivo (Cote and Lewis, 2008). However, MUS81-EME1 and Slx1p-Slx4p prepared in E. coli are largely devoid of activity toward static HJs (Ciccia et al, 2003;Fricke and Brill, 2003) leading to the conclusion that these enzymes alone are not efficient HJ resolvases.…”