Electrostatic Drivers of GPx4 Interactions with Membrane, Lipids, and DNA.

Glutathione peroxidase 4 (GPx4) serves as the only enzyme that protects membranes through the reduction of lipid hydroperoxides, preventing membrane oxidative damage and cell death through ferroptosis. Recently, GPx4 has gained attention as a therapeutic target for cancer through inhibition and as a target for inflammatory diseases through activation. In addition, GPx4 isoforms perform several distinct moonlighting functions including cysteine cross-linking of protamines during sperm cell chromatin remodeling, a function for which molecular and structural details are undefined. Despite the importance in biology, disease, and potential for drug development, little is known about GPx4 functional interactions at high resolution. This study presents the first NMR assignments of GPx4, and the electrostatic interaction of GPx4 with the membrane is characterized. Mutagenesis reveals the cationic patch residues that are key to membrane binding and stabilization. The cationic patch is observed to be important in binding headgroups of highly anionic cardiolipin. A novel lipid binding site is observed adjacent to the catalytic site and may enable protection of lipid-headgroups from oxidative damage. Arachidonic acid is also found to engage with GPx4, while cholesterol did not display any interaction. The cationic patch residues were also found to enable DNA binding, the first observation of this interaction. Electrostatic DNA binding explains a mechanism for the nuclear isoform of GPx4 to target DNA-bound protamines and to potentially reduce oxidatively damaged DNA. Together, these results highlight the importance of electrostatics in the function of GPx4 and illuminate how the multifunctional enzyme is able to fill multiple biological roles.

A role for condensin in mediating transcriptional adaptation to environmental stimuli.

Nuclear organisation shapes gene regulation; however, the principles by which three-dimensional genome architecture influences gene transcription are incompletely understood. Condensin is a key architectural chromatin constituent, best known for its role in mitotic chromosome condensation. Yet at least a subset of condensin is bound to DNA throughout the cell cycle. Studies in various organisms have reported roles for condensin in transcriptional regulation, but no unifying mechanism has emerged. Here, we use rapid conditional condensin depletion in the budding yeast Saccharomyces cerevisiae to study its role in transcriptional regulation. We observe a large number of small gene expression changes, enriched at genes located close to condensin-binding sites, consistent with a possible local effect of condensin on gene expression. Furthermore, nascent RNA sequencing reveals that transcriptional down-regulation in response to environmental stimuli, in particular to heat shock, is subdued without condensin. Our results underscore the multitude by which an architectural chromosome constituent can affect gene regulation and suggest that condensin facilitates transcriptional reprogramming as part of adaptation to environmental changes.

In vitro ameliorative effects of ellagic acid on vitality, motility and DNA quality in human spermatozoa.

Oxidative stress (OS) plays a significant role in the etiology of male infertility, resulting in the impairment of male reproduction. This condition, characterized by an imbalance in the levels of oxidizing and antioxidant species in the seminal fluid, has a harmful impact on sperm functions and DNA integrity. The present study aimed to evaluate the anti-genotoxic action of ellagic acid, a polyphenolic molecule of natural origin having a powerful antigenotoxic, anti-inflammatory and antiproliferative role. An OS condition was induced in vitro by incubating normozoospermic human semen samples in benzene for 45, 60 and 90 min. DNA integrity was evaluated by terminal deoxynucleotidyl transferase dUTP nick end labeling assay, RAPD-PCR was performed to calculate the genome template stability, while the percentage of intracellular reactive oxygen species (ROS) was assessed by the 2', 7'-dichlorofluorescein assay. Our results showed that ellagic acid has a consistent protective effect on DNA integrity, as well as on sperm vitality and motility, by counteracting generation of intracellular ROS. The results of this study suggest ellagic acid as a suitable molecule to protect sperm DNA from oxidative stress, with a potentially significant translational impact on the management of the male infertility.

Exploiting replicative stress in gynecological cancers as a therapeutic strategy.

Elevated levels of replicative stress in gynecological cancers arising from uncontrolled oncogenic activation, loss of key tumor suppressors, and frequent defects in the DNA repair machinery are an intrinsic vulnerability for therapeutic exploitation. The presence of replication stress activates the DNA damage response and downstream checkpoint proteins including ataxia telangiectasia and Rad3 related kinase (ATR), checkpoint kinase 1 (CHK1), and WEE1-like protein kinase (WEE1), which trigger cell cycle arrest while protecting and restoring stalled replication forks. Strategies that increase replicative stress while lowering cell cycle checkpoint thresholds may allow unrepaired DNA damage to be inappropriately carried forward in replicating cells, leading to mitotic catastrophe and cell death. Moreover, the identification of fork protection as a key mechanism of resistance to chemo- and poly (ADP-ribose) polymerase inhibitor therapy in ovarian cancer further increases the priority that should be accorded to the development of strategies targeting replicative stress. Small molecule inhibitors designed to target the DNA damage sensors, such as inhibitors of ataxia telangiectasia-mutated (ATM), ATR, CHK1 and WEE1, impair smooth cell cycle modulation and disrupt efficient DNA repair, or a combination of the above, have demonstrated interesting monotherapy and combinatorial activity, including the potential to reverse drug resistance and have entered developmental pipelines. Yet unresolved challenges lie in balancing the toxicity profile of these drugs in order to achieve a suitable therapeutic index while maintaining clinical efficacy, and selective biomarkers are urgently required. Here we describe the premise for targeting of replicative stress in gynecological cancers and discuss the clinical advancement of this strategy.

Emerging strategies to target cancer metabolism and improve radiation therapy outcomes.

Cancer-specific metabolic changes support the anabolic needs of the rapidly growing tumor, maintain a favorable redox balance, and help cells adapt to microenvironmental stresses like hypoxia and nutrient deprivation. Radiation is extensively applied in a large number of cancer treatment protocols but despite its curative potential, radiation resistance and treatment failures pose a serious problem. Metabolic control of DNA integrity and genomic stability can occur through multiple processes, encompassing cell cycle regulation, nucleotide synthesis, epigenetic regulation of gene activity, and antioxidant defenses. Given the important role of metabolic pathways in oxidative damage responses, it is necessary to assess the potential for tumor-specific radiosensitization by novel metabolism-targeted therapies. Additionally, there are opportunities to identify molecular and functional biomarkers of vulnerabilities to combination treatments, which could then inform clinical decisions. Here, we present a curated list of metabolic pathways in the context of ionizing radiation responses. Glutamine metabolism influences DNA damage responses by mechanisms such as synthesis of nucleotides for DNA repair or of glutathione for ROS detoxification. Repurposed oxygen consumption inhibitors have shown promising radiosensitizing activity against murine model tumors and are now in clinical trials. Production of 2-hydroxy glutarate by isocitrate dehydrogenase1/2 neomorphic oncogenic mutants interferes with the function of α-ketoglutarate-dependent enzymes and modulates Ataxia Telangiectasia Mutated (ATM) signaling and glutathione pools. Radiation-induced oxidative damage to membrane phospholipids promotes ferroptotic cell loss and cooperates with immunotherapies to improve tumor control. In summary, there are opportunities to enhance the efficacy of radiotherapy by exploiting cell-inherent vulnerabilities and dynamic microenvironmental components of the tumor.

An Acidic-Microenvironment-Driven DNA Nanomachine Enables Specific ATP Imaging in the Extracellular Milieu of Tumor.

Extracellular ATP is an emerging target for cancer treatment because it is a key messenger for shaping the tumor microenvironment (TME) and regulating tumor progression. However, it remains a great challenge to design biochemical probes for targeted imaging of extracellular ATP in the TME. A TME-driven DNA nanomachine (Apt-LIP) that permits spatially controlled imaging of ATP in the extracellular milieu of tumors with ultrahigh signal-to-background ratio is reported. It operates in response to the mild acidity in the TME with the pH (low) insertion peptide (pHLIP) module, thus allowing the specific anchoring of the structure-switching signaling aptamer unit to the membrane of tumor cells for "off-on" fluorescence imaging of the extracellular ATP. Apt-LIP allows for acidity driven visualization of different extracellular concentrations of exogenous ATP, as well as the monitoring of endogenous ATP release from cells. Furthermore, it is demonstrated that Apt-LIP represents a promising platform for the specific imaging of the extracellular ATP in both primary and metastatic tumors. Ultimately, since diverse aptamers are obtained through in vitro selection, this design strategy can be further applied for precise detection of various extracellular targets in the TME.

Chloroquine reduces hypercoagulability in pancreatic cancer through inhibition of neutrophil extracellular traps.

BACKGROUND: The hypercoagulable state associated with pancreatic adenocarcinoma (PDA) results in increased risk of venous thromboembolism, leading to substantial morbidity and mortality. Recently, neutrophil extracellular traps (NETs), whereby activated neutrophils release their intracellular contents containing DNA, histones, tissue factor, high mobility group box 1 (HMGB1) and other components have been implicated in PDA and in cancer-associated thrombosis. METHODS: Utilizing an orthotopic murine PDA model in C57/Bl6 mice and patient correlative samples, we studied the role of NETs in PDA hypercoagulability and targeted this pathway through treatment with the NET inhibitor chloroquine. PAD4 and RAGE knockout mice, deficient in NET formation, were used to study the role of NETs in platelet aggregation, release of tissue factor and hypercoagulability. Platelet aggregation was assessed using collagen-activated impedance aggregometry. Levels of circulating tissue factor, the initiator of extrinsic coagulation, were measured using ELISA. Thromboelastograms (TEGs) were performed to assess hypercoagulability and changes associated with treatment. Correlative data and samples from a randomized clinical trial of preoperative gemcitabine/nab-paclitaxel with and without hydroxychloroquine were studied and the impact of treatment on venous thromboembolism (VTE) rate was evaluated. RESULTS: The addition of NETs to whole blood stimulated platelet activation and aggregation. DNA and the receptor for advanced glycation end products (RAGE) were necessary for induction of NET associated platelet aggregation. PAD4 knockout tumor-burdened mice, unable to form NETs, had decreased aggregation and decreased circulating tissue factor. The NET inhibitor chloroquine reduces platelet aggregation, reduces circulating tissue factor and decreases hypercoagulability on TEG. Review of correlative data from patients treated on a randomized protocol of preoperative chemotherapy with and without hydroxychloroquine demonstrated a reduction in peri-operative VTE rate from 30 to 9.1% with hydroxychloroquine that neared statistical significance (p = 0.053) despite the trial not being designed to study VTE. CONCLUSION: NETs promote hypercoagulability in murine PDA through stimulation of platelets and release of tissue factor. Chloroquine inhibits NETs and diminishes hypercoagulability. These findings support clinical study of chloroquine to lower rates of venous thromboembolism in patients with cancer. TRIAL REGISTRATION: This study reports correlative data from two clinical trials that registered with clinicaltrials.gov, NCT01128296 (May 21, 2010) and NCT01978184 (November 7, 2013).

Naked mole rat cells display more efficient excision repair than mouse cells.

Naked mole rat (NMR) is the long-lived and tumor-resistant rodent. NMRs possess multiple adaptations that may contribute to longevity and cancer-resistance. However, whether NMRs have more efficient DNA repair have not been directly tested. Here we compared base excision repair (BER) and nucleotide excision repair (NER) systems in extracts from NMR and mouse fibroblasts after UVC irradiation. Transcript levels of the key repair enzymes demonstrated in most cases higher inducibility in the mouse vs the NMR cells. Ratios of repair enzymes activities in the extracts somewhat varied depending on post-irradiation time. NMR cell extracts were 2-3-fold more efficient at removing the bulky lesions, 1.5-3-fold more efficient at removing uracil, and about 1.4-fold more efficient at cleaving the AP-site than the mouse cells, while DNA polymerase activities being as a whole higher in the mouse demonstrate different patterns of product distribution. The level of poly(ADP-ribose) synthesis was 1.4-1.8-fold higher in the NMR cells. Furthermore, NMR cell extracts displayed higher binding of PARP1 to DNA probes containing apurinic/apyrimidinic site or photo-reactive DNA lesions. Cumulatively, our results suggest that the NMR has more efficient excision repair systems than the mouse, which may contribute to longevity and cancer resistance of this species.

A novel transcript isoform of STING that sequesters cGAMP and dominantly inhibits innate nucleic acid sensing.

STING is a core adaptor in innate nucleic acid sensing in mammalian cells, on which different sensing pathways converge to induce type I interferon (IFN) production. Particularly, STING is activated by 2'3'-cGAMP, a cyclic dinucleotide containing mixed phosphodiester linkages and produced by cytoplasmic DNA sensor cGAS. Here, we reported on a novel transcript isoform of STING designated STING-ß that dominantly inhibits innate nucleic acid sensing. STING-ß without transmembrane domains was widely expressed at low levels in various human tissues and viral induction of STING-ß correlated inversely with IFN-ß production. The expression of STING-ß declined in patients with lupus, in which type I IFNs are commonly overproduced. STING-ß suppressed the induction of IFNs, IFN-stimulated genes and other cytokines by various immunostimulatory agents including cyclic dinucleotides, DNA, RNA and viruses, whereas depletion of STING-ß showed the opposite effect. STING-ß interacted with STING-α and antagonized its antiviral function. STING-ß also interacted with TBK1 and prevented it from binding with STING-α, TRIF or other transducers. In addition, STING-ß bound to 2'3'-cGAMP and impeded its binding with and activation of STING-α, leading to suppression of IFN-ß production. Taken together, STING-ß sequesters 2'3'-cGAMP second messenger and other transducer molecules to inhibit innate nucleic acid sensing dominantly.

Effect of Various Treatment Modes of Experimental Mammary Gland Tumor on Structure of Anterior Mediastinal Lymph Nodes.

The effects of various treatment modes on the morphology of anterior mediastinal lymph nodes were examined in female Wistar rats with chemically provoked breast cancer. Adjuvant chemotherapy impaired filtration barrier potential of the anterior mediastinal lymph nodes, which manifested in increased volume of sinuses, reduced volumes of lymphoid nodules with germinal centers and thymus-dependent regions, down-regulated proliferative activity of lymphoid cells in B-cell zone and paracortex, and diminished macrophage score in all zones. Intraperitoneal injection of double-stranded DNA preparation (5 mg/kg) activated the humoral and cellular immune responses manifested by morphological alterations in anterior mediastinal lymph nodes observed in parallel with a decrease of medullary sinuses volume: enhancement of lymphocyte volume and lymphocyte score in paracortex, mantle zone expansion, and an increase of volume of the light centers in lymphoid nodules paralleled with diminished proliferative activity in them.

Collapse of DNA in packaging and cellular transport.

The dawn of molecular biology and recombinant DNA technology arose from our ability to manipulate DNA, including the process of collapse of long extended DNA molecules into nanoparticles of approximately 100 nm diameter. This condensation process is important for the packaging of DNA in the cell and for transporting DNA through the cell membrane for gene therapy. Multivalent cations, such as natural polyamines (spermidine and spermine), were initially recognized for their ability to provoke DNA condensation. Current research is targeted on molecules such as linear and branched polymers, oligopeptides, polypeptides and dendrimers that promote collapse of DNA to nanometric particles for gene therapy and on the energetics of DNA packaging.

AIM2 Inflammasome Is Critical for dsDNA-Induced IL-1ß Secretion in Human Dental Pulp Cells.

The AIM2 inflammasome pathway has been determined to play an important role in cellular immune defense against bacterial and viral infections; however, its function and regulatory mechanism in human dental pulp cells (HDPCs) during pulpitis remains poorly understood. In this study, we explored whether the AIM2 inflammasome pathway was activated in HDPCs in response to dsDNA and defined its role in regulating IL-1ß secretion. We demonstrated that stimulation with IFN-γ and cytoplasmic DNA significantly activated the AIM2 inflammasome and increased IL-1ß secretion in HDPCs. Moreover, AIM2 overexpression significantly up-regulated both cleaved Caspase-1 expression and IL-1ß release in HDPCs, while suppression of ASC and Caspase-1 resulted in down-regulation of cleaved Caspase-1 and IL-1ß secretion. These results suggest that Caspase-1-dependent IL-1ß processing and secretion require the AIM2 inflammasome pathway in HDPCs and that the AIM2 inflammasome pathway is critical for regulation of the dental pulp immune response.

Effect of the acrosome reaction on the efficiency of sperm-mediated DNA transfer.

Sperm-mediated gene transfer (SMGT) is based on the ability of spermatozoa to bind exoge- nous DNA and transfer it into oocytes by fertilization. However, SMGT is still undergoing opti- mization to improve its efficiency to produce transgenic animals. The acrosome reaction is neces- sary for spermatozoa to carry the exogenous DNA into oocytes. In this study, the effect of the acrosome reaction on the efficiency of spermatozoa carrying exogenous DNA was evalua- ted. The results showed that the efficiency of the acrosome reaction was significantly higher (p⟨0.05) after incubation with 50 µmol/L progesterone compared to incubation without proges- terone. It was significantly higher (p⟨0.05) in the 20, 40, and 60 min of progesterone treatment groups than in the 0 min treatment group. The spermatozoa were further incubated with cyanine dye Cy5 labeled DNA (Cy5-DNA) for 30 min at 37°C, and positive fluorescence signals were detected after the acrosome reaction was induced by progesterone at concentrations of 0 and 50 µmol/L for 40 min. The percentage of positive Cy5-DNA signals in spermatozoa was 96.61±2.06% and 97.51±2.03% following exposure to 0 and 50 µmol/L progesterone, respective- ly. The percentage of partial spermatozoa heads observed following combination with Cy5-DNA was 39.73±3.03% and 56.88±3.12% following exposure to 0 and 50 µmol/L progesterone, respec- tively. The ratio of positively stained spermatozoa combined with exogenous DNA showed no reduction after the acrosome reaction. These results suggest that the acrosome reaction might not be the key factor affecting the efficiency of SMGT.

DNA helix: the importance of being AT-rich.

The AT-rich DNA is mostly associated with condensed chromatin, whereas the GC-rich sequence is preferably located in the dispersed chromatin. The AT-rich genes are prone to be tissue-specific (silenced in most tissues), while the GC-rich genes tend to be housekeeping (expressed in many tissues). This paper reports another important property of DNA base composition, which can affect repertoire of genes with high AT content. The GC-rich sequence is more liable to mutation. We found that Spearman correlation between human gene GC content and mutation probability is above 0.9. The change of base composition even in synonymous sites affects mutation probability of nonsynonymous sites and thus of encoded proteins. There is a unique type of housekeeping genes, which are especially unsafe when prone to mutation. Natural selection which usually removes deleterious mutations, in the case of these genes only increases the hazard because it can descend to suborganismal (cellular) level. These are cell cycle-related genes. In accordance with the proposed concept, they have low GC content of synonymous sites (despite them being housekeeping). The gene-centred protein interaction enrichment analysis (PIEA) showed the core clusters of genes whose interactants are modularly enriched in genes with AT-rich synonymous codons. This interconnected network is involved in double-strand break repair, DNA integrity checkpoints and chromosome pairing at mitosis. The damage of these genes results in genome and chromosome instability leading to cancer and other 'error catastrophes'. Reducing the nonsynonymous mutations, the usage of AT-rich synonymous codons can decrease probability of cancer by above 20-fold.

Tetrahelical structural family adopted by AGCGA-rich regulatory DNA regions.

Here we describe AGCGA-quadruplexes, an unexpected addition to the well-known tetrahelical families, G-quadruplexes and i-motifs, that have been a focus of intense research due to their potential biological impact in G- and C-rich DNA regions, respectively. High-resolution structures determined by solution-state nuclear magnetic resonance (NMR) spectroscopy demonstrate that AGCGA-quadruplexes comprise four 5'-AGCGA-3' tracts and are stabilized by G-A and G-C base pairs forming GAGA- and GCGC-quartets, respectively. Residues in the core of the structure are connected with edge-type loops. Sequences of alternating 5'-AGCGA-3' and 5'-GGG-3' repeats could be expected to form G-quadruplexes, but are shown herein to form AGCGA-quadruplexes instead. Unique structural features of AGCGA-quadruplexes together with lower sensitivity to cation and pH variation imply their potential biological relevance in regulatory regions of genes responsible for basic cellular processes that are related to neurological disorders, cancer and abnormalities in bone and cartilage development.

Cytosolic DNA Promotes Signal Transducer and Activator of Transcription 3 (STAT3) Phosphorylation by TANK-binding Kinase 1 (TBK1) to Restrain STAT3 Activity.

Cytosolic DNA can elicit beneficial as well as undesirable immune responses. For example, viral or microbial DNA triggers cell-intrinsic immune responses to defend against infections, whereas aberrant cytosolic accumulation of self-DNA results in pathological conditions, such as autoimmunity. Given the importance of these DNA-provoked responses, a better understanding of their molecular mechanisms is needed. Cytosolic DNA engages stimulator of interferon genes (STING) to activate TANK-binding kinase 1 (TBK1), which subsequently phosphorylates the transcription factor interferon regulatory factor 3 (IRF3) to promote interferon expression. Recent studies have reported that additional transcription factors, including nuclear factor κB (NF-κB) and signal transducer and activator of transcription 6 (STAT6), are also activated by cytosolic DNA, suggesting that cytosolic DNA-induced gene expression is orchestrated by multiple factors. Here we show that cytosolic DNA activates STAT3, another member of the STAT family, via an autocrine mechanism involving interferon ß (IFNß) and IL-6. Additionally, we observed a novel cytosolic DNA-induced phosphorylation at serine 754 in the transactivation domain of STAT3. Upon cytosolic DNA stimulation, Ser754 is directly phosphorylated by TBK1 in a STING-dependent manner. Moreover, Ser754 phosphorylation inhibits cytosolic DNA-induced STAT3 transcriptional activity and selectively reduces STAT3 target genes that are up-regulated in response to cytosolic DNA. Taken together, our results suggest that cytosolic DNA-induced STAT3 activation via IFNß and IL-6 is restrained by Ser754 phosphorylation of STAT3. Our findings reveal a new signaling axis downstream of the cytosolic DNA pathway and suggest potential interactions between innate immune responses and STAT3-driven oncogenic pathways.

Evidence for cell-free nucleic acids as continuously arising endogenous DNA mutagens.

There is extensive literature to show that nucleic acids can be taken up by cells under experimental conditions and that foetal DNA can be detected in maternal tissues. The uptaken DNA can integrate into host cell genomes and can be transcribed and translated into proteins. They can also cause chromosomal damage and karyotype alterations. Cell-free nucleic acids (cfNAs)-based non-invasive DNA diagnostic techniques are being extensively researched in the field of cancer with the potential to advance new prognostic parameters and direct treatment decisions. However, whether extracellular cfNAs that are released into circulation from dying cells as a consequence of normal physiology have any functional significance has not been explored. A recent study has demonstrated that circulating cfNAs have the ability to cause DNA damage and mutagenesis by illegitimately integrating into healthy cells of the body, thereby acting as mobile genetic elements. Fluorescently-labeled cfNAs isolated from sera of cancer patients and healthy volunteers were shown to be readily taken up by host cells followed by activation of a DNA-damage-repair-response which led their large scale integration into the host cell genomes. The latter caused dsDNA breaks and apoptosis in cells in vitro and in those of vital organs when injected intravenously into mice. Cell-free chromatin was consistently more active than cell-free DNA, while cfNAs derived from cancer patients were significantly more active than those from healthy volunteers. This study suggests that circulating extracellular cfNAs act as physiological continuously arising DNA mutagens with implications for ageing, cancer and a host of other degenerative human pathologies.

DNA repair pathway choice at various conditions immediately post irradiation.

PURPOSE: To clarify which DNA double-strand break repair pathway, non-homologous end-joining (NHEJ), homologous recombination repair (HRR) or both, plays a key role in potentially lethal damage repair (PLDR). METHODS AND MATERIALS: Combining published data and our new potentially lethal damage repair (PLDR) data, we explain whether similar to sublethal damage repair (SLDR), PLDR also mainly depends on NHEJ versus HRR. The PLDR data used the same cell lines: wild type, HRR or NHEJ-deficient fibroblast cells, as those SLDR data published by our laboratory previously. The PLDR condition that we used was as commonly described by many other groups: the cells were collected immediately or overnight post ionizing radiation for colony formation after cultured to a plateau phase with a low concentration of serum medium. RESULTS: Enough data from other groups and our lab showed that wild type or HRR-deficient cells had efficient PLDR, but NHEJ deficient cells did not. CONCLUSION: NHEJ contributes more to PLDR than HRR in mammalian cells, which is similar to SLDR. Since both SLDR and PLDR are relevant to clinical tumor status while undergoing radiotherapy, such clarification may benefit radiotherapy in the near future.

SMC complexes: from DNA to chromosomes.

SMC (structural maintenance of chromosomes) complexes - which include condensin, cohesin and the SMC5-SMC6 complex - are major components of chromosomes in all living organisms, from bacteria to humans. These ring-shaped protein machines, which are powered by ATP hydrolysis, topologically encircle DNA. With their ability to hold more than one strand of DNA together, SMC complexes control a plethora of chromosomal activities. Notable among these are chromosome condensation and sister chromatid cohesion. Moreover, SMC complexes have an important role in DNA repair. Recent mechanistic insight into the function and regulation of these universal chromosomal machines enables us to propose molecular models of chromosome structure, dynamics and function, illuminating one of the fundamental entities in biology.