Recombination Step Research Articles

DNA sequence differences are determinants of meiotic recombination outcome

Meiotic recombination is essential for producing healthy gametes, and also generates genetic diversity. DNA double-strand break (DSB) formation is the initiating step of meiotic recombination, producing, among other outcomes, crossovers between homologous chromosomes (homologs), which provide physical links to guide accurate chromosome segregation. The parameters influencing DSB position and repair are thus crucial determinants of reproductive success and genetic diversity. Using Schizosaccharomyces pombe, we show that the distance between sequence polymorphisms across homologs has a strong impact on meiotic recombination rate. The closer the sequence polymorphisms are to each other across the homologs the fewer recombination events were observed. In the immediate vicinity of DSBs, sequence polymorphisms affect the frequency of intragenic recombination events (gene conversions). Additionally, and unexpectedly, the crossover rate of flanking markers tens of kilobases away from the sequence polymorphisms was affected by their relative position to each other amongst the progeny having undergone intragenic recombination. A major regulator of this distance-dependent effect is the MutSα-MutLα complex consisting of Msh2, Msh6, Mlh1, and Pms1. Additionally, the DNA helicases Rqh1 and Fml1 shape recombination frequency, although the effects seen here are largely independent of the relative position of the sequence polymorphisms.

Recruitment of Rec8, Pds5 and Rad61/Wapl to meiotic homolog pairing, recombination, axis formation and S-phase.

We have explored the meiotic roles of cohesin modulators Pds5 and Rad61/Wapl, in relation to one another, and to meiotic kleisin Rec8, for homolog pairing, all physically definable steps of recombination, prophase axis length and S-phase progression, in budding yeast. We show that Pds5 promotes early steps of recombination and thus homolog pairing, and also modulates axis length, with both effects independent of a sister chromatid. [Pds5+Rec8] promotes double-strand break formation, maintains homolog bias for crossover formation and promotes S-phase progression. Oppositely, the unique role of Rad61/Wapl is to promote non-crossover recombination by releasing [Pds5+Rec8]. For this effect, Rad61/Wapl probably acts to maintain homolog bias by preventing channeling into sister interactions. Mysteriously, each analyzed molecule has one role that involves neither of the other two. Overall, the presented findings suggest that Pds5’s role in maintenance of sister chromatid cohesion during the mitotic prophase-analogous stage of G2/M is repurposed during meiosis prophase to promote interactions between homologs.

A New Suite of Allelic-Exchange Vectors for the Scarless Modification of Proteobacterial Genomes.

Despite the advent of new techniques for genetic engineering of bacteria, allelic exchange through homologous recombination remains an important tool for genetic analysis. Currently, sacB-based vector systems are often used for allelic exchange, but counterselection escape, which prevents isolation of cells with the desired mutation, occasionally limits their utility. To circumvent this, we engineered a series of "pTOX" allelic-exchange vectors. Each plasmid encodes one of a set of inducible toxins, chosen for their potential utility in a wide range of medically important proteobacteria. A codon-optimized rhaS transcriptional activator with a strong synthetic ribosome-binding site enables tight toxin induction even in organisms lacking an endogenous rhamnose regulon. Expression of the gene encoding blue AmilCP or magenta TsPurple nonfluorescent chromoprotein facilitates monitoring of successful single- and double-crossover events using these vectors. The versatility of these vectors was demonstrated by deleting genes in Serratia marcescens, Escherichia coli O157:H7, Enterobacter cloacae, and Shigella flexneri Finally, pTOX was used to characterize the impact of disruption of all combinations of the 3 paralogous S. marcescens peptidoglycan amidohydrolases on chromosomal ampC β-lactamase activity and the corresponding β-lactam antibiotic resistance. Mutation of multiple amidohydrolases was necessary for high-level ampC derepression and β-lactam resistance. These data suggest why β-lactam resistance may emerge during treatment less frequently in S. marcescens than in other AmpC-producing pathogens, like E. cloacae Collectively, our findings suggest that the pTOX vectors should be broadly useful for genetic engineering of Gram-negative bacteria.IMPORTANCE Targeted modification of bacterial genomes is critical for genetic analysis of microorganisms. Allelic exchange is a technique that relies on homologous recombination to replace native loci with engineered sequences. However, current allelic-exchange vectors often enable only weak selection for successful homologous recombination. We developed a suite of new allelic-exchange vectors, pTOX, which were validated in several medically important proteobacteria. They encode visible nonfluorescent chromoproteins that enable easy identification of colonies bearing integrated vectors and permit stringent selection for the second step of homologous recombination. We demonstrate the utility of these vectors by using them to investigate the effect of inactivation of Serratia marcescens peptidoglycan amidohydrolases on β-lactam antibiotic resistance.

A one-step reduced mechanism for near-limit hydrogen combustion with general stoichiometry

A one-step reduced mechanism for hydrogen combustion, previously developed for fuel-lean flames, is extended to apply for all equivalence ratios under near-limit conditions by taking into consideration two additional recombination steps that are important under fuel-rich conditions. It is found that the crossover temperature that appears in the cutoff factor is smaller under fuel-rich conditions. Besides improving insights, the results can be beneficial in speeding computations.

A Multiprotein Complex Regulates Interference-Sensitive Crossover Formation in Rice.

In most eukaryotes, a set of conserved proteins that are collectively termed ZMM proteins (named for molecular zipper 1 [ZIP1], ZIP2, ZIP3, and ZIP4, MutS homologue 4 [MSH4] and MSH5, meiotic recombination 3, and sporulation 16 [SPO16] in yeast [Saccharomyces cerevisiae]) are essential for the formation of the majority of meiotic crossovers (COs). Recent reports indicated that ZIP2 acts together with SPO16 and ZIP4 to control CO formation through recognizing and stabilizing early recombination intermediates in budding yeast. However, whether this mechanism is conserved in plants is not clear. Here, we characterized the functions of SHORTAGE OF CHIASMATA 1 (OsSHOC1; ZIP2 ortholog) and PARTING DANCERS (OsPTD; SPO16 ortholog) and their interactions with other ZMM proteins in rice (Oryza sativa). We demonstrated that disruption of OsSHOC1 caused a reduction of CO numbers to ∼83% of wild-type CO numbers, whereas synapsis and early meiotic recombination steps were not affected. Furthermore, OsSHOC1 interacts with OsPTD, which is responsible for the same set of CO formations as OsSHOC1. In addition, OsSHOC1 and OsPTD are required for the normal loading of other ZMM proteins, and conversely, the localizations of OsSHOC1 and OsPTD were also affected by the absence of OsZIP4 and human enhancer of invasion 10 in rice (OsHEI10). OsSHOC1 interacts with OsZIP4 and OsMSH5, and OsPTD interacts with OsHEI10. Furthermore, bimolecular fluorescence complementation and yeast-three hybrid assays demonstrated that OsSHOC1, OsPTD, OsHEI10, and OsZIP4 were able to form various combinations of heterotrimers. Moreover, statistical and genetic analysis indicated that OsSHOC1 and OsPTD are epistatic to OsHEI10 and OsZIP4 in meiotic CO formation. Taken together, we propose that OsSHOC1, OsPTD, OsHEI10, and OsZIP4 form multiple protein complexes that have conserved functions in promoting class I CO formation.

ERCC1/XPF Is Important for Repair of DNA Double-Strand Breaks Containing Secondary Structures

SummaryThe structure-specific endonuclease ERCC1/XPF plays an important role in nucleotide excision repair and interstrand cross-link repair. In this study, we identified new functions of ERCC1/XPF in DNA double-strand break (DSB) repair. We found that the conserved function of ERCC1/XPF to remove non-homologous sequences at DSBs is a rate-limiting step for homologous recombination in mammalian cells, and more importantly, we uncovered an indispensable role of ERCC1/XPF in repair of DSBs containing DNA secondary structures, including the structure-prone AT-rich DNA sequences derived from common fragile sites and G-quadruplexes (G4s). We also demonstrated a synthetic lethal interaction of XPF with DNA translocase FANCM that is involved in removing DNA secondary structures. Furthermore, inactivation of XPF sensitizes FANCM-deficient cells to G4-interacting compounds. These results suggest an important function of ERCC1/XPF in protecting DNA secondary structures and provide a rationale for targeted treatment of FANCM-deficient tumors through inhibition of XPF.

EXOSC10 is required for RPA assembly and controlled DNA end resection at DNA double-strand breaks

The exosome is a ribonucleolytic complex that plays important roles in RNA metabolism. Here we show that the exosome is necessary for the repair of DNA double-strand breaks (DSBs) in human cells and that RNA clearance is an essential step in homologous recombination. Transcription of DSB-flanking sequences results in the production of damage-induced long non-coding RNAs (dilncRNAs) that engage in DNA-RNA hybrid formation. Depletion of EXOSC10, an exosome catalytic subunit, leads to increased dilncRNA and DNA-RNA hybrid levels. Moreover, the targeting of the ssDNA-binding protein RPA to sites of DNA damage is impaired whereas DNA end resection is hyper-stimulated in EXOSC10-depleted cells. The DNA end resection deregulation is abolished by transcription inhibitors, and RNase H1 overexpression restores the RPA recruitment defect caused by EXOSC10 depletion, which suggests that RNA clearance of newly synthesized dilncRNAs is required for RPA recruitment, controlled DNA end resection and assembly of the homologous recombination machinery.

Charge Generation in Monolayer Transition Metal Dichalcogenides

At the monolayer level, many layered 2D transition metal dichalcogenides (TMDCs) are direct bandgap semiconductors in which photo-excitation creates strongly bound excitons. To incorporate these excitonic semiconductors into solar energy harvesting and conversion devices, it is critical to dissociate excitons to produce long-lived free charge carriers. There are still many open questions regarding the fundamental steps of exciton dissociation and subsequent recombination of charge carriers within 2D TMDCs. These include the roles of defects and traps in localizing charges, the types of interfaces that facilitate fast charge separation and slow recombination, and the role of charge diffusion/delocalization in overcoming the Coulomb binding energy following charge separation. In this talk, I will discuss our efforts at answering some of these questions using a number of 2D TMDC model systems and interfaces. We observe long-lived charge generation in certain neat 2D TMDCs that can be related to specific growth-related defects. Charge generation can also be enhanced by creating interfaces with the appropriate energetics for separating electrons and holes, and the lifetime of the charge-separated state is tied to the degree to which the carrier(s) can escape the interface through diffusion and/or delocalization. These studies provide insight into harnessing the potential of monolayer 2D TMDCs in solar energy harvesting and solar fuels applications.

The Antiresection Activity of the X Protein Encoded by Hepatitis Virus B

Chronic infection of hepatitis B virus (HBV) is associated with an increased incidence of hepatocellular carcinoma (HCC). HBV encodes an oncoprotein, hepatitis B x protein (HBx), that is crucial for viral replication and interferes with multiple cellular activities including gene expression, histone modifications, and genomic stability. To date, it remains unclear how disruption of these activities contributes to hepatocarcinogenesis. Here, we report that HBV exhibits antiresection activity by disrupting DNA end resection, thus impairing the initial steps of homologous recombination (HR). This antiresection activity occurs in primary human hepatocytes undergoing a natural viral infection–replication cycle as well as in cells with integrated HBV genomes. Among the seven HBV‐encoded proteins, we identified HBx as the sole viral factor that inhibits resection. By disrupting an evolutionarily conserved Cullin4A–damage‐specific DNA binding protein 1–RING type of E3 ligase, CRL4WDR70, through its H‐box, we show that HBx inhibits H2B monoubiquitylation at lysine 120 at double‐strand breaks, thus reducing the efficiency of long‐range resection. We further show that directly impairing H2B monoubiquitylation elicited tumorigenesis upon engraftment of deficient cells in athymic mice, confirming that the impairment of CRL4WDR70 function by HBx is sufficient to promote carcinogenesis. Finally, we demonstrate that lack of H2B monoubiquitylation is manifest in human HBV‐associated HCC when compared with HBV‐free HCC, implying corresponding defects of epigenetic regulation and end resection. Conclusion: The antiresection activity of HBx induces an HR defect and genomic instability and contributes to tumorigenesis of host hepatocytes.

On the feasibility of bifunctional hydrogen oxidation on Ni and NiCu surfaces

Nickel is a promising alternative to noble metal catalysts for hydrogen electrocatalysis in alkaline membrane fuel cells and electrolyzers. To boost its electrocatalytic activity, it is often associated with other metals, like Cu. In this work, we combine density functional theory (DFT), Monte Carlo calculations and kinetic modeling in order to shed light on the origin of the experimentally observed activity enhancement on bimetallic NiCu nanoparticles containing ca. 5% of Cu compared to pure Ni (Topics in Catalysis, 58, (2015), 1181–1192; J. Electroanal. Chem., 783, (2016), 146–151). It is shown that the bifunctional HOR mechanism, where Had and OHad recombine to form water, is not viable on the monometallic Ni electrode because of the strong hydrogen adsorption and the high activation energy barrier of the recombination reaction. On bimetallic NiCu surfaces, DFT calculations predict a significant weakening of Had adsorption energy as well as a decrease of the activation barrier of the recombination reaction for ca. 50% Cu surface coverage. Monte Carlo simulations reveal that the surface of NiCu nanoparticles is enriched in Cu atoms even for a small (ca. 5%) Cu atomic fraction in the bulk. Kinetic modeling suggests that the experimental data for NiCu nanoparticles can be well reproduced either considering fast recombination step (bifunctional mechanism) or fast (10-fold enhancement compared to pure Ni) Volmer step (Heyrovsky-Volmer mechanism).

Real-time Observation of the DNA Strand Exchange Reaction Mediated by Rad51.

The DNA strand exchange reaction mediated by Rad51 is a critical step of homologous recombination. In this reaction, Rad51 forms a nucleoprotein filament on single-stranded DNA (ssDNA) and captures double-stranded DNA (dsDNA) non-specifically to interrogate it for a homologous sequence. After encountering homology, Rad51 catalyzes DNA strand exchange to mediate pairing of the ssDNA with the complementary strand of the dsDNA. This reaction is highly regulated by numerous accessary proteins in vivo. Although conventional biochemical assays have been successfully employed to examine the role of such accessory protein in vitro, kinetic analysis of intermediate formation and its progression into a final product has proven challenging due to the unstable and transient nature of the reaction intermediates. To observe these reaction steps directly in solution, fluorescence resonance energy transfer (FRET)-based real-time observation systems of this reaction were established. Kinetic analysis of real-time observations shows that the DNA strand exchange reaction mediated by Rad51 obeys a three-step reaction model involving the formation of a three-strand DNA intermediate, maturation of this intermediate, and the release of ssDNA from the mature intermediate. The Swi5-Sfr1 complex, an accessary protein conserved in eukaryotes, strongly enhances the second and third steps of this reaction. The FRET-based assays presented here enable us to uncover the molecular mechanisms through which recombination accessary proteins stimulate the DNA strand exchange activity of Rad51. The primary goal of this protocol is to enhance the repertoire of techniques available to researchers in the field of homologous recombination, particularly those working with proteins from species other than Schizosaccharomyces pombe, so that the evolutionary conservation of the findings presented herein can be determined.

Mutation in DDM1 inhibits the homology directed repair of double strand breaks.

In all organisms, DNA damage must be repaired quickly and properly, as it can be lethal for cells. Because eukaryotic DNA is packaged into nucleosomes, the structural units of chromatin, chromatin modification is necessary during DNA damage repair and is achieved by histone modification and chromatin remodeling. Chromatin remodeling proteins therefore play important roles in the DNA damage response (DDR) by modifying the accessibility of DNA damage sites. Here, we show that mutation in a SWI2/SNF2 chromatin remodeling protein (DDM1) causes hypersensitivity in the DNA damage response via defects in single-strand annealing (SSA) repair of double-strand breaks (DSBs) as well as in the initial steps of homologous recombination (HR) repair. ddm1 mutants such as ddm1-1 and ddm1-2 exhibited increased root cell death and higher DSB frequency compared to the wild type after gamma irradiation. Although the DDM1 mutation did not affect the expression of most DDR genes, it did cause substantial decrease in the frequency of SSA as well as partial inhibition in the γ-H2AX and Rad51 induction, the initial steps of HR. Furthermore, global chromatin structure seemed to be affected by DDM1 mutations. These results suggest that DDM1 is involved in the homology directed repair such as SSA and HR, probably by modifying chromatin structure.

Induction of a Toxin-Antitoxin Gene Cassette under High Hydrostatic Pressure Enables Markerless Gene Disruption in the Hyperthermophilic Archaeon Pyrococcus yayanosii.

The discovery of hyperthermophiles has dramatically changed our understanding of the habitats in which life can thrive. However, the extreme high temperatures in which these organisms live have severely restricted the development of genetic tools. The archaeon Pyrococcus yayanosii A1 is a strictly anaerobic and piezophilic hyperthermophile that is an ideal model for studies of extreme environmental adaptation. In the present study, we identified a high hydrostatic pressure (HHP)-inducible promoter (P hhp ) that controls target gene expression under HHP. We developed an HHP-inducible toxin-antitoxin cassette (HHP-TAC) containing (i) a counterselectable marker in which a gene encoding a putative toxin (virulence-associated protein C [PF0776 {VapC}]) controlled by the HHP-inducible promoter was used in conjunction with the gene encoding antitoxin PF0775 (VapB), which was fused to a constitutive promoter (P hmtB ), and (ii) a positive marker with the 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase-encoding gene from P. furiosus controlled by the constitutive promoter P gdh The HHP-TAC was constructed to realize markerless gene disruption directly in P. yayanosii A1 in rich medium. The pop-out recombination step was performed using an HHP-inducible method. As proof, the PYCH_13690 gene, which encodes a 4-α-glucanotransferase, was successfully deleted from the strain P. yayanosii A1. The results showed that the capacity for starch hydrolysis in the Δ1369 mutant decreased dramatically compared to that in the wild-type strain. The inducible toxin-antitoxin system developed in this study greatly increases the genetic tools available for use in hyperthermophiles.IMPORTANCE Genetic manipulations in hyperthermophiles have been studied for over 20 years. However, the extremely high temperatures under which these organisms grow have limited the development of genetic tools. In this study, an HHP-inducible promoter was used to control the expression of a toxin. Compared to sugar-inducible and cold-shock-inducible promoters, the HHP-inducible promoter rarely has negative effects on the overall physiology and central metabolism of microorganisms, especially piezophilic hyperthermophiles. Previous studies have used auxotrophic strains as hosts, which may interfere with studies of adaptation and metabolism. Using an inducible toxin-antitoxin (TA) system as a counterselectable marker enables the generation of a markerless gene disruption strain without the use of auxotrophic mutants and counterselection with 5-fluoroorotic acid. TA systems are widely distributed in bacteria and archaea and can be used to overcome the limitations of high growth temperatures and dramatically extend the selectivity of genetic tools in hyperthermophiles.

Development of a dual-antimicrobial counterselection method for markerless genetic engineering of bacterial genomes.

Markerless genetic engineering of bacterial genomes is commonly performed by two-step homologous recombination methods using vectors carrying flanking regions of the target gene for site-specific vector integration and counterselection markers to provide positive selection pressure on the second recombination step resulting in vector excision. Here, we provide the proof-of-principle of a novel counterselection method that exploits antagonistic activities between bactericidal and bacteriostatic antibiotics and which can provide selection pressure on the second recombination step by selective killing of bacteria retaining the antibiotic selection marker. This method was optimized for the bacterial pathogens Listeria monocytogenes and Neisseria meningitidis by screening for antagonistic activities between the bactericidal aminoglycosides kanamycin, streptomycin, and gentamicin in combination with the bacteriostatic antibiotics chloramphenicol and erythromycin. The largest difference in selective killing of both L. monocytogenes and N. meningitidis containing an antibiotic selection marker versus wild-type bacteria was observed for the combination of erythromycin, gentamicin, and ermC as antibiotic selection marker. Therefore, this combination was used to generate two markerless deletion mutants for both L. monocytogenes and N. meningitidis. After applying the dual-antimicrobial selection pressure on cultures during the second recombination step, surviving colonies were replica plated on agar with and without erythromycin. On average, 12-13% of the randomly selected bacterial colonies had lost the selection marker due to a second recombination event and approximately half of these colonies were the desired markerless in-frame deletion mutants. Therefore, this method proved to be easy and fast and should be applicable to a wide variety of bacterial species.

Isotopic Shifts of the Frumkin and Temkin Adsorption Isotherms of H and D at Pt/Alkaline Solution Interfaces: Analysis Using the Phase-Shift Method

Due to the superposition of various effects at electrocatalyst/solution interfaces, the Frumkin and Temkin adsorption isotherms of H and D are not readily determined using conventional methods. The phase-shift method is a unique electrochemical impedance spectroscopy technique for studying the linear relationship between the phase shift (90° ≥ −φ ≥ 0°) for the optimum intermediate frequency vs potential (E) behavior and the fractional coverage (0 ≤ θ ≤ 1) for adsorption vs potential (E) behavior. The Frumkin and Temkin adsorption isotherms (θ vs E) of H and D and their isotopic shifts at Pt/0.1 M LiOH (H2O, D2O) solution interfaces are determined using the phase-shift method. Over the θ range (i.e., 1 ≥ θ ≥ 0), the kinetic isotope effect (KH/D) is 3.1 to 3.5 and the standard Gibbs energy (ΔGθ0) of D is 2.8 to 3.1 kJ mol−1 greater than that of H. The bond dissociation energy for Pt−D2O is greater than that for Pt−H2O. The rate-determining steps are determined by the recombination step at low θ or E and electrochemical desorption step at high θ or E, sequentially. The isotopic shifts of the Frumkin and Temkin adsorption isotherms of H and D and related electrode kinetic effects are clearly distinguished.

Variation in RAD51 details a hub of functions: opportunities to advance cancer diagnosis and therapy.

Loss of genome stability is one of the hallmarks of the enabling characteristics of cancer development. Homologous recombination is a DNA repair process that often breaks down as a prelude to developing cancer. Conversely, homologous recombination can be the Achilles’ heel in common anti-cancer therapies, which are effective by inducing irreparable DNA damage. Here, we review recent structural and functional studies of RAD51, the protein that catalyzes the defining step of homologous recombination: homology recognition and DNA strand exchange. Specific mutations can be linked to structural changes and known essential functions. Additional RAD51 interactions and functions may be revealed. The identification of viable mutations in this essential protein may help define the range of activity and interactions needed. All of this information provides opportunities to fine-tune existing therapies based on homologous recombination status, guide diagnosis, and hopefully develop new clinical tools.

Competition between green self-trapped-exciton and red non-bridging-oxygen emissions in SiO2 under interband excitation

The knowledge advancement in the physics of silicon dioxide has promoted ground-breaking progress, from microelectronics to fibre optics. However, the SiO2 exciton decay mechanism is still mostly unrevealed. Here, we analyse the temperature dependence of interband-excited luminescence and the reflectivity by means of synchrotron radiation on a wide selection of SiO2 materials. This enables us to decouple the band-to-band recombination steps from non-radiative decay pathways that typically mask the relaxation mechanisms. We show that band-to-band excitations decay into two competitive correlated channels leading to green and red luminescence so far ascribed to independent transitions. Here we discuss the assignment to a dual relaxation route involving either ‘free’ or ‘interacting’ non-bridging-oxygen sites. Such an interpretation suggests an explanation for the elusive non-bridging-oxygen centres in quartz. The reflectivity spectra finally demonstrates a general relationship between exciton spectral position and bandwidth in SiO2 and clarifies the role of disorder in exciton localization.

Shu complex SWS1-SWSAP1 promotes early steps in mouse meiotic recombination

The DNA-damage repair pathway homologous recombination (HR) requires factors that promote the activity of strand-exchange protein RAD51 and its meiosis-specific homolog DMC1. Here we show that the Shu complex SWS1-SWSAP1, a candidate for one such HR regulator, is dispensable for mouse viability but essential for male and female fertility, promoting the assembly of RAD51 and DMC1 on early meiotic HR intermediates. Only a fraction of mutant meiocytes progress to form crossovers, which are crucial for chromosome segregation, demonstrating crossover homeostasis. Remarkably, loss of the DNA damage checkpoint kinase CHK2 rescues fertility in females without rescuing crossover numbers. Concomitant loss of the BRCA2 C terminus aggravates the meiotic defects in Swsap1 mutant spermatocytes, suggesting an overlapping role with the Shu complex during meiotic HR. These results demonstrate an essential role for SWS1-SWSAP1 in meiotic progression and emphasize the complex interplay of factors that ensure recombinase function.

BLM can regulate cataract progression by influencing cell vitality and apoptosis

Age-related cataract (ARC) is the most common cause of severe visual impairment and blindness. The precise mechanisms of ARC are not completely understood, but it is well accepted that oxidative damage plays an important role in the disease pathogenesis. BLM, the key enzyme of the double-strand break repair (DSBR) pathway, is part of a family of DNA unwinding enzymes and has a crucial role in multiple steps of the DNA recombination, replication and repair processes. We have recently shown that BLM-rs1063147 is initially associated with nuclear ARC in a cross-section study. Therefore, we wanted to study the effects of BLM on ARC progression. In ARC patients, BLM transcription in lens capsules was decreased, so did the BLM protein, and after UVB irradiation, BLM mRNA and protein levels were increased in SRA01/04 cells. Upon silencing BLM in SRA01/04 cells and rat lens, cell vitality and apoptosis were altered, and the rat lens opacification was considerable. In conclusion, BLM can regulate cataract progression by influencing cell vitality and apoptosis.

Variation in RAD51 details a hub of functions: opportunities to advance cancer diagnosis and therapy.

Loss of genome stability is one of the hallmarks of the enabling characteristics of cancer development. Homologous recombination is a DNA repair process that often breaks down as a prelude to developing cancer. Conversely, homologous recombination can be the Achilles' heel in common anti-cancer therapies, which are effective by inducing irreparable DNA damage. Here, we review recent structural and functional studies of RAD51, the protein that catalyzes the defining step of homologous recombination: homology recognition and DNA strand exchange. Specific mutations can be linked to structural changes and known essential functions. Additional RAD51 interactions and functions may be revealed. The identification of viable mutations in this essential protein may help define the range of activity and interactions needed. All of this information provides opportunities to fine-tune existing therapies based on homologous recombination status, guide diagnosis, and hopefully develop new clinical tools.