Folding of cohesin's coiled coil is important for Scc2/4-induced association with chromosomes.

Cohesin's association with and translocation along chromosomal DNAs depend on an ATP hydrolysis cycle driving the association and subsequent release of DNA. This involves DNA being 'clamped' by Scc2 and ATP-dependent engagement of cohesin's Smc1 and Smc3 head domains. Scc2's replacement by Pds5 abrogates cohesin's ATPase and has an important role in halting DNA loop extrusion.

A Protocol for Assaying the ATPase Activity of Recombinant Cohesin Holocomplexes.

Cohesin and other members of the structural maintenance of chromosomes (SMC)-kleisin family such as condensin and Smc5-6, as well as central players in genome function and structure such as topoisomerases, DNA and RNA polymerases, and DNA repair enzymes contain nucleotide binding domains (NBD) which bind and eventually cleave ATP. The released energy is harnessed in various ways by these enzymes in order to fulfill their essential functions. However, unlike other enzymes, Smc-kleisin complexes-well sized, elongated and multisubunit in nature-have only recently been purified as holocomplexes.

Scc2 Is a Potent Activator of Cohesin's ATPase that Promotes Loading by Binding Scc1 without Pds5.

Cohesin organizes DNA into chromatids, regulates enhancer-promoter interactions, and confers sister chromatid cohesion. Its association with chromosomes is regulated by hook-shaped HEAT repeat proteins that bind Scc1, namely Scc3, Pds5, and Scc2. Unlike Pds5, Scc2 is not a stable cohesin constituent but, as shown here, transiently replaces Pds5.

Chromosome Biology: The Smc-Kleisin Enzymology Finally Comes of Age.

Cohesin and condensin are Smc-kleisin complexes responsible for shaping our chromosomes. Despite extensive genetic and genomic information available on their function, their biochemistry has been hard to study. Two recent studies finally bring exciting new insights into their enzymology.

The Cohesin Ring Uses Its Hinge to Organize DNA Using Non-topological as well as Topological Mechanisms.

As predicted by the notion that sister chromatid cohesion is mediated by entrapment of sister DNAs inside cohesin rings, there is perfect correlation between co-entrapment of circular minichromosomes and sister chromatid cohesion. In most cells where cohesin loads without conferring cohesion, it does so by entrapment of individual DNAs. However, cohesin with a hinge domain whose positively charged lumen is neutralized loads and moves along chromatin despite failing to entrap DNAs.

Structurally Guided In Vivo Crosslinking.

The focus of modern molecular biology on protein structure and function has reached unparalleled levels. Whether interacting with nucleic acids or other proteins, protein contacts are the basis for fine-tuning all cellular processes. It is for this reason imperative that protein interactions are studied in ways that reflect actual events taking place inside living cells.

Chromosome Biology: The Sight of DNA, at Last!

Chromosomes are shaped by the combined function of the condensin and cohesin Smc-kleisin complexes. After more than two decades of research in this field, a new study finally sheds light on how these machines might interact with their DNA substrates.

Evolution of condensin and cohesin complexes driven by replacement of Kite by Hawk proteins.

Mitotic chromosome condensation, sister chromatid cohesion, and higher order folding of interphase chromatin are mediated by condensin and cohesin, eukaryotic members of the SMC (structural maintenance of chromosomes)-kleisin protein family. Other members facilitate chromosome segregation in bacteria [1]. A hallmark of these complexes is the binding of the two ends of a kleisin subunit to the apices of V-shaped Smc dimers, creating a tripartite ring capable of entrapping DNA (Figure 1A).

Structural Insights into Ring Formation of Cohesin and Related Smc Complexes.

Cohesin facilitates sister chromatid cohesion through the formation of a large ring structure that encircles DNA. Its function relies on two structural maintenance of chromosomes (Smc) proteins, which are found in almost all organisms tested, from bacteria to humans. In accordance with their ubiquity, Smc complexes, such as cohesin, condensin, Smc5-6, and the dosage compensation complex, affect almost all processes of DNA homeostasis.

Releasing Activity Disengages Cohesin's Smc3/Scc1 Interface in a Process Blocked by Acetylation.

Sister chromatid cohesion conferred by entrapment of sister DNAs within a tripartite ring formed between cohesin's Scc1, Smc1, and Smc3 subunits is created during S and destroyed at anaphase through Scc1 cleavage by separase. Cohesin's association with chromosomes is controlled by opposing activities: loading by Scc2/4 complex and release by a separase-independent releasing activity as well as by cleavage. Coentrapment of sister DNAs at replication is accompanied by acetylation of Smc3 by Eco1, which blocks releasing activity and ensures that sisters remain connected.

Closing the cohesin ring: structure and function of its Smc3-kleisin interface.

Through their association with a kleisin subunit (Scc1), cohesin's Smc1 and Smc3 subunits are thought to form tripartite rings that mediate sister chromatid cohesion. Unlike the structure of Smc1/Smc3 and Smc1/Scc1 interfaces, that of Smc3/Scc1 is not known. Disconnection of this interface is thought to release cohesin from chromosomes in a process regulated by acetylation.

Pds5 promotes and protects cohesin acetylation.

Cohesin's Smc1 and Smc3 subunits form V-shaped heterodimers, the nucleotide binding domains (NBDs) of which bind the C- and N-terminal domains, respectively, of the α-kleisin subunit, forming a large tripartite ring within in which sister DNAs are entrapped, and thereby held together (sister chromatid cohesion). During replication, establishment of stable cohesion is dependent on Eco1-mediated acetylation of Smc3's NBD, which is thought to prevent dissociation of α-kleisin from Smc3, thereby locking shut a "DNA exit gate." How Scc3 and Pds5, regulatory subunits bound to α-kleisin, regulate cohesion establishment and maintenance is poorly understood.

A yeast catabolic enzyme controls transcriptional memory.

It has been postulated that chromatin modifications can persist through mitosis and meiosis, thereby securing memory of transcriptional states. Whether these chromatin marks can self-propagate in progeny independently of relevant trans-acting factors is an important question in phenomena related to epigenesis. "Adaptive cellular memory" displayed by yeast cells offers a convenient system to address this question.

The Tup1 corepressor directs Htz1 deposition at a specific promoter nucleosome marking the GAL1 gene for rapid activation.

The SWR1 complex (SWR1-C)-dependent deposition of the histone variant Htz1 on promoter nucleosomes is typical of Saccharomyces cerevisiae genes whose expression is frequently reprogrammed. Although this epigenetic marking is of significant physiological importance, the determinants of Htz1 deposition, the conditions that set off SWR1-C occupancy, and the implications of Htz1 in transcriptional initiation are issues that remain unresolved. In this report, we addressed these questions by investigating the GAL1 promoter.

The Snf1 kinase controls glucose repression in yeast by modulating interactions between the Mig1 repressor and the Cyc8-Tup1 co-repressor.

Among lower eukaryotes, glucose repression is a conserved, widely spread mechanism regulating carbon catabolism. The yeast Snf1 kinase, the Mig1 DNA-binding repressor and the Mig1-interacting co-repressor complex Cyc8(Ssn6)-Tup1 are central components of this pathway. Previous experiments suggested that cytoplasmic translocation of Mig1, upon its phosphorylation by Snf1 in the nucleus, is the key regulatory step for releasing glucose repression.