A model for Scc2p stimulation of cohesin's ATPase and its inhibition by acetylation of Smc3p.

The evolutionarily conserved cohesin complex mediates sister chromatid cohesion and facilitates mitotic chromosome condensation, DNA repair, and transcription regulation. These biological functions require cohesin's two ATPases, formed by the Smc1p and Smc3p subunits. Cohesin's ATPase activity is stimulated by the Scc2p auxiliary factor.

Cohesin architecture and clustering in vivo.

Cohesin helps mediate sister chromatid cohesion, chromosome condensation, DNA repair, and transcription regulation. We exploited proximity-dependent labeling to define the in vivo interactions of cohesin domains with DNA or with other cohesin domains that lie within the same or in different cohesin complexes. Our results suggest that both cohesin's head and hinge domains are proximal to DNA, and cohesin structure is dynamic with differential folding of its coiled coil regions to generate butterfly confirmations.

Cohesin residency determines chromatin loop patterns.

The organization of chromatin into higher order structures is essential for chromosome segregation, the repair of DNA-damage, and the regulation of gene expression. Using Micro-C XL to detect chromosomal interactions, we observed the pervasive presence of cohesin-dependent loops with defined positions throughout the genome of budding yeast, as seen in mammalian cells. In early S phase, cohesin stably binds to cohesin associated regions (CARs) genome-wide.

The spatial regulation of condensin activity in chromosome condensation.

Condensin mediates chromosome condensation, which is essential for proper chromosome segregation during mitosis. Prior to anaphase of budding yeast, the ribosomal DNA (RDN) condenses to a thin loop that is distinct from the rest of the chromosomes. We provide evidence that the establishment and maintenance of this RDN condensation requires the regulation of condensin by Cdc5p (polo) kinase.

Communication between distinct subunit interfaces of the cohesin complex promotes its topological entrapment of DNA.

Cohesin mediates higher order chromosome structure. Its biological activities require topological entrapment of DNA within a lumen(s) formed by cohesin subunits. The reversible dissociation of cohesin's Smc3p and Mcd1p subunits is postulated to form a regulated gate that allows DNA entry and exit into the lumen.

Desiccation tolerance: an unusual window into stress biology.

Climate change has accentuated the importance of understanding how organisms respond to stresses imposed by changes to their environment, like water availability. Unusual organisms, called anhydrobiotes, can survive loss of almost all intracellular water. Desiccation tolerance of anhydrobiotes provides an unusual window to study the stresses and stress response imposed by water loss.

Intermediate step of cohesin's ATPase cycle allows cohesin to entrap DNA.

Cohesin is a four-subunit ATPase in the family of structural maintenance of chromosomes (SMC). Cohesin promotes sister chromatid cohesion, chromosome condensation, DNA repair, and transcription regulation. Cohesin performs these functions as a DNA tether and potentially a DNA-based motor.

Genome-wide Map of R-Loop-Induced Damage Reveals How a Subset of R-Loops Contributes to Genomic Instability.

DNA-RNA hybrids associated with R-loops promote DNA damage and genomic instability. The capacity of hybrids at different genomic sites to cause DNA damage was not known, and the mechanisms leading from hybrid to damage were poorly understood. Here, we adopt a new strategy to map and characterize the sites of hybrid-induced damage genome-wide in budding yeast.

Synergy between the small intrinsically disordered protein Hsp12 and trehalose sustain viability after severe desiccation.

Anhydrobiotes are rare microbes, plants and animals that tolerate severe water loss. Understanding the molecular basis for their desiccation tolerance may provide novel insights into stress biology and critical tools for engineering drought-tolerant crops. Using the anhydrobiote, budding yeast, we show that trehalose and Hsp12, a small intrinsically disordered protein (sIDP) of the hydrophilin family, synergize to mitigate completely the inviability caused by the lethal stresses of desiccation.

A role for the Smc3 hinge domain in the maintenance of sister chromatid cohesion.

Cohesin is a conserved protein complex required for sister chromatid cohesion, chromosome condensation, DNA damage repair, and regulation of transcription. Although cohesin functions to tether DNA duplexes, the contribution of its individual domains to this activity remains poorly understood. We interrogated the Smc3p subunit of cohesin by random insertion mutagenesis.

Cohesin Function in Cohesion, Condensation, and DNA Repair Is Regulated by Wpl1p via a Common Mechanism in .

Cohesin tethers DNA to mediate sister chromatid cohesion, chromosome condensation, and DNA repair. How the cell regulates cohesin to perform these distinct functions remains to be elucidated. One cohesin regulator, Wpl1p, was characterized in as a promoter of efficient cohesion and an inhibitor of condensation.

Tardigrades Use Intrinsically Disordered Proteins to Survive Desiccation.

Tardigrades are microscopic animals that survive a remarkable array of stresses, including desiccation. How tardigrades survive desiccation has remained a mystery for more than 250 years. Trehalose, a disaccharide essential for several organisms to survive drying, is detected at low levels or not at all in some tardigrade species, indicating that tardigrades possess potentially novel mechanisms for surviving desiccation.

RNase H enables efficient repair of R-loop induced DNA damage.

R-loops, three-stranded structures that form when transcripts hybridize to chromosomal DNA, are potent agents of genome instability. This instability has been explained by the ability of R-loops to induce DNA damage. Here, we show that persistent R-loops also compromise DNA repair.

Differential roles of the RNases H in preventing chromosome instability.

DNA:RNA hybrids can lead to DNA damage and genome instability. This damage can be prevented by degradation of the RNA in the hybrid by two evolutionarily conserved enzymes, RNase H1 and H2. Indeed, RNase H-deficient cells have increased chromosomal rearrangements.

Back to the Future: Mutant Hunts Are Still the Way To Go.

Innumerable breakthroughs in many fundamental areas of biology have come from unbiased screens and selections for mutations, either across the genome or within a gene. However, long-standing hurdles to key elements of mutant hunts (mutagenesis, phenotypic characterization, and linkage of phenotype to genotype) have limited the organisms in which mutant hunts could be used. These hurdles are now being eliminated by an explosion of new technologies.

S1-DRIP-seq identifies high expression and polyA tracts as major contributors to R-loop formation.

R loops form when transcripts hybridize to homologous DNA on chromosomes, yielding a DNA:RNA hybrid and a displaced DNA single strand. R loops impact the genome of many organisms, regulating chromosome stability, gene expression, and DNA repair. Understanding the parameters dictating R-loop formation in vivo has been hampered by the limited quantitative and spatial resolution of current genomic strategies for mapping R loops.

Single-Molecule Imaging Reveals a Collapsed Conformational State for DNA-Bound Cohesin.

Cohesin is essential for the hierarchical organization of the eukaryotic genome and plays key roles in many aspects of chromosome biology. The conformation of cohesin bound to DNA remains poorly defined, leaving crucial gaps in our understanding of how cohesin fulfills its biological functions. Here, we use single-molecule microscopy to directly observe the dynamic and functional characteristics of cohesin bound to DNA.

The ATPases of cohesin interface with regulators to modulate cohesin-mediated DNA tethering.

Cohesin tethers together regions of DNA, thereby mediating higher order chromatin organization that is critical for sister chromatid cohesion, DNA repair and transcriptional regulation. Cohesin contains a heterodimeric ATP-binding Cassette (ABC) ATPase comprised of Smc1 and Smc3 ATPase active sites. These ATPases are required for cohesin to bind DNA.

Interallelic complementation provides functional evidence for cohesin-cohesin interactions on DNA.

The cohesin complex (Mcd1p, Smc1p, Smc3p, and Scc3p) has multiple roles in chromosome architecture, such as promoting sister chromatid cohesion, chromosome condensation, DNA repair, and transcriptional regulation. The prevailing embrace model for sister chromatid cohesion posits that a single cohesin complex entraps both sister chromatids. We report interallelic complementation between pairs of nonfunctional mcd1 alleles (mcd1-1 and mcd1-Q266) or smc3 alleles (smc3-42 and smc3-K113R).

The Yin and Yang of R-loop biology.

RNA performs diverse functions in cells, directing translation, modulating transcription and catalyzing enzymatic reactions. Remarkably RNA can also anneal to its genomic template co- or post-transcriptionally to generate an RNA-DNA hybrid and a displaced single-stranded DNA. These unusual nucleic acid structures are called R-loops.

Increasing intracellular trehalose is sufficient to confer desiccation tolerance to Saccharomyces cerevisiae.

Diverse organisms capable of surviving desiccation, termed anhydrobiotes, include species from bacteria, yeast, plants, and invertebrates. However, most organisms are sensitive to desiccation, likely due to an assortment of different stresses such as protein misfolding and aggregation, hyperosmotic stress, membrane fracturing, and changes in cell volume and shape leading to an overcrowded cytoplasm and metabolic arrest. The exact stress(es) that cause lethality in desiccation-sensitive organisms and how the lethal stresses are mitigated in desiccation-tolerant organisms remain poorly understood.

A conserved domain in the scc3 subunit of cohesin mediates the interaction with both mcd1 and the cohesin loader complex.

The Structural Maintenance of Chromosome (SMC) complex, termed cohesin, is essential for sister chromatid cohesion. Cohesin is also important for chromosome condensation, DNA repair, and gene expression. Cohesin is comprised of Scc3, Mcd1, Smc1, and Smc3.

Trehalose is a versatile and long-lived chaperone for desiccation tolerance.

Background: Diverse organisms across taxa are desiccation tolerant, capable of surviving extreme water loss. Remarkably, desiccation tolerant organisms can survive years without water. However, the molecular mechanisms underlying this rare trait are poorly understood.

A novel mechanism for the establishment of sister chromatid cohesion by the ECO1 acetyltransferase.

Cohesin complex mediates cohesion between sister chromatids, which promotes high-fidelity chromosome segregation. Eco1p acetylates the cohesin subunit Smc3p during S phase to establish cohesion. The current model posits that this Eco1p-mediated acetylation promotes establishment by abrogating the ability of Wpl1p to destabilize cohesin binding to chromosomes.

ROCC, a conserved region in cohesin's Mcd1 subunit, is essential for the proper regulation of the maintenance of cohesion and establishment of condensation.

Cohesin helps orchestrate higher-order chromosome structure, thereby promoting sister chromatid cohesion, chromosome condensation, DNA repair, and transcriptional regulation. To elucidate how cohesin facilitates these diverse processes, we mutagenized Mcd1p, the kleisin regulatory subunit of budding yeast cohesin. In the linker region of Mcd1p, we identified a novel evolutionarily conserved 10-amino acid cluster, termed the regulation of cohesion and condensation (ROCC) box.