Loss of DHX36/G4R1, a G4 resolvase, drives genome instability and regulates innate immune gene expression in cancer cells.

G-quadruplexes (G4s) are four-stranded alternative secondary structures formed by guanine-rich nucleic acids and are prevalent across the human genome. G4s are enzymatically resolved by specialized helicases. Previous in vitro studies showed that DEAH-box helicase 36 (DHX36/G4R1/RHAU) has the highest specificity and affinity for G4 structures.

Protection of double-Holliday junctions ensures crossing over during meiosis.

Chromosomal linkages formed through crossover recombination are essential for accurate segregation of homologous chromosomes during meiosis. The DNA events of recombination are linked to structural components of meiotic chromosomes. Imperatively, the biased resolution of double-Holliday junction intermediates (dHJs) into crossovers occurs within the synaptonemal complex (SC), the meiosis-specific structure that mediates end-to-end synapsis of homologs during the pachytene stage.

Breakage of cytoplasmic chromosomes by pathological DNA base excision repair.

Chromothripsis is a catastrophic mutational process that promotes tumorigenesis and causes congenital disease. Chromothripsis originates from aberrations of nuclei called micronuclei or chromosome bridges. These structures are associated with fragile nuclear envelopes that spontaneously rupture, leading to DNA damage when chromatin is exposed to the interphase cytoplasm.

Regulated Proteolysis of MutSγ Controls Meiotic Crossing Over.

Crossover recombination is essential for accurate chromosome segregation during meiosis. The MutSγ complex, Msh4-Msh5, facilitates crossing over by binding and stabilizing nascent recombination intermediates. We show that these activities are governed by regulated proteolysis.

Monitoring Recombination During Meiosis in Budding Yeast.

Homologous recombination is fundamental to sexual reproduction, facilitating accurate segregation of homologous chromosomes at the first division of meiosis, and creating novel allele combinations that fuel evolution. Following initiation of meiotic recombination by programmed DNA double-strand breaks (DSBs), homologous pairing and DNA strand exchange form joint molecule (JM) intermediates that are ultimately resolved into crossover and noncrossover repair products. Physical monitoring of the DNA steps of meiotic recombination in Saccharomyces cerevisiae (budding yeast) cultures undergoing synchronous meiosis has provided seminal insights into the molecular basis of meiotic recombination and affords a powerful tool for dissecting the molecular roles of recombination factors.

Pervasive and essential roles of the Top3-Rmi1 decatenase orchestrate recombination and facilitate chromosome segregation in meiosis.

The Bloom's helicase ortholog, Sgs1, plays central roles to coordinate the formation and resolution of joint molecule intermediates (JMs) during meiotic recombination in budding yeast. Sgs1 can associate with type-I topoisomerase Top3 and its accessory factor Rmi1 to form a conserved complex best known for its unique ability to decatenate double-Holliday junctions. Contrary to expectations, we show that the strand-passage activity of Top3-Rmi1 is required for all known functions of Sgs1 in meiotic recombination, including channeling JMs into physiological crossover and noncrossover pathways, and suppression of non-allelic recombination.

Native/Denaturing two-dimensional DNA electrophoresis and its application to the analysis of recombination intermediates.

Two-dimensional (2D) gel electrophoresis employs distinct electrophoretic conditions to better resolve complex mixtures of molecules. In combination with Southern analysis, 2D agarose gel electrophoresis is routinely employed to detect and analyze DNA intermediates that arise during the replication and repair of chromosomes. By separating intermediates into their component single-strands, native/denaturing 2D gels can reveal structure that is not apparent under native conditions alone.

Delineation of joint molecule resolution pathways in meiosis identifies a crossover-specific resolvase.

At the final step of homologous recombination, Holliday junction-containing joint molecules (JMs) are resolved to form crossover or noncrossover products. The enzymes responsible for JM resolution in vivo remain uncertain, but three distinct endonucleases capable of resolving JMs in vitro have been identified: Mus81-Mms4(EME1), Slx1-Slx4(BTBD12), and Yen1(GEN1). Using physical monitoring of recombination during budding yeast meiosis, we show that all three endonucleases are capable of promoting JM resolution in vivo.

Temporally and biochemically distinct activities of Exo1 during meiosis: double-strand break resection and resolution of double Holliday junctions.

The Rad2/XPG family nuclease, Exo1, functions in a variety of DNA repair pathways. During meiosis, Exo1 promotes crossover recombination and thereby facilitates chromosome segregation at the first division. Meiotic recombination is initiated by programmed DNA double-strand breaks (DSBs).