Search

The deep mining process of North China type coalfields is highly threatened by the threat of water damage from the floor limestone aquifer. By arranging grouting holes reasonably to inject a large amount of slurry into the aquifer that directly threatens the safety of coal seam mining, making the strong aquifer a weak aquifer or an impermeable layer is the main means to solve such water damage problems. In microfracture grouting engineering, the slurry-rock mass coupling effect has a significant impact on the diffusion process of slurry. To this end, the interaction between slurry and rock mass and the diffusion mechanism of slurry during high-pressure grouting of coal seam floor aquifers was studied, a single fracture grouting diffusion theoretical model was established that considers the slurry flow-rock mass deformation coupling effect, based on the viscosity time varying Bingham slurry diffusion equation and fracture aperture control equation. The spatial distribution characteristics of slurry pressure and fracture aperture in the slurry diffusion direction were analyzed, and the effect rules of slurry-rock mass coupling effect on slurry diffusion was revealed, and the results were compared with the grouting model with constant fracture aperture. The results showed that the attenuation trend of slurry pressure and fracture aperture in the slurry diffusion direction was consistent, and both had obvious nonlinear characteristics, and the attenuation was faster in the fracture entrance area. The degree of slurry-rock mass coupling effect decreased with the increase of fracture aperture, and the design value of grouting pressure will be too high if fracture aperture was small and the slurry-rock mass coupling effect was not considered. The grouting pressure became the main controlling factor affecting the slurry diffusion distance gradually as the fracture aperture increased. By comparing the theoretical results with an example of grouting transformation of the limestone aquifer in the lower coal seam floor of Luxi coal mine, the validity of the theoretical model was verified.

To enhance the understanding of yield-related traits in tetraploid wheat, it is crucial to investigate and identify genes that govern superior yield characteristics. This study utilized the wheat55K single nucleotide polymorphism array to genotype a recombinant inbred line (RIL) population consisting of 120 lines developed through the crossbreeding of two tetraploid wheat varieties, Qin Hei-1 (QH-1) and Durum Wheat (DW). An investigation and analysis were conducted on 11 yield-related traits, including peduncle length (PL), neck length (NL), spike length (SL), flowering date (FD), heading date (HD), thousand-kernel weight (TKW), kernel area ratio (KAR), kernel circumference (KC), kernel length (KL), kernel width (KW), and kernel length–width ratio (KL-WR), over a period of three years in two locations, Yang Ling, Shaanxi, and Lin He, Inner Mongolia. The analysis identified nine stable loci among eight agronomic traits, named QSL.QD-1A.1, QNL.QD-4B.2, QPL.QD-4B.1, QFD.QD-2B, QHD.QD-2B.1, QHD.QD-4B, QKC.QD-4B.2, QKL-WR.QD-4B.6, and QKL.QD-4B.2. Among them, the additive effects of three QTLs, QSL.QD-1A.1, QNL.QD-4B.2, and QFD.QD-2B, were positive, indicating that the enhancing alleles at these loci were derived from the parent line QH-1. These three QTLs showed significant positive effects on the phenotypes of the population materials. Furthermore, potential functional genes were identified within the mapping intervals of QSL.QD-1A.1 and QNL.QD-4B.2, which regulate the development of spike length and neck length, respectively. These results provide potential QTLs and candidate genes, which broaden the genetic basis of agronomic traits related to yield, such as SL, NL, PL, and FD, and benefits for wheat breeding and improvement.

Abstract Water inrush is one of the most dangerous disasters in coal mining. Due to the large-scale mining and complicated hydrogeological conditions, thousands of deaths and huge economic losses have been caused by water inrush disasters in China. There are two main factors determining the occurrence of water inrush: water source and water-conducting pathway. Research on the formation mechanism of the water-conducting pathway is the main direction to prevent and control the water inrush, and the seepage mechanism of rock mass during the formation of the water-conducting pathway is the key for the research on the water inrush mechanism. This paper provides a state-of-the-art review of seepage mechanisms during water inrush from three aspects, i.e., mechanisms of stress-seepage coupling, flow regime transformation and rock erosion. Through numerical methods and experimental analysis, the evolution law of stress and seepage fields in the process of water inrush is fully studied; the fluid movement characteristics under different flow regimes are clearly summarized; the law of particle initiation and migration in the process of water inrush is explored, and the effect of rock erosion on hydraulic and mechanical properties of the rock media is also studied. Finally, some limitations of current research are analyzed, and the suggestions for future research on water inrush are proposed in this review.

The present study was conducted to investigate the tensile strength characteristics of polypropylene (PP) fiber reinforced soil with different fiber dispersion, content and aspect ratio. In order to investigate this, the experimental programme was comprised by the test with a wide range of fiber content (0.35%, 0.60%, 0.85%), fiber aspect ratio (150, 225, 350), and mix patterns (discrete or random distribution). The results indicated that increases in fiber content caused an increment in the tensile strength whether discrete or random distribution. The increasing extent of tensile strength was different with increase of fiber aspect ratio under different fiber mix patterns. From experimental data, a genetic programming (GP) model was proposed for analyzing tensile strength contrast of the two mix patterns. In addition, the sensitive analysis of three inputs showed that aspect ratio has the greatest influence on the forecasting model. The effectiveness of the GP model was validated by the test results, and the robust model developed would provide a theoretical support for roadbase designing and construction which were reinforced with PP fibers.

Wheat is one of the most important food crops in the world and drought can severely impact on wheat productivity. The identification and deployment of genes for improved water use efficiency (WUE) can help alleviate yield loss under water limitation. In this study, a high-density genetic linkage map of wheat recombinant inbred lines (Ningchun 4 x Ningchun 27) containing 8751 specific locus amplified fragment (SLAF) tags (including 14757 SNPs), with a total map distance of 1685 cM and an average inter-marker map distance of 0.19 cM was constructed by SLAF-seq technology. The economic yield WUE and nine related traits under three water treatments was monitored over four years. The results showed that loci conditioning WUE were also associated with grain carbon isotope discrimination (CID), flag leaf chlorophyll content, plant height, 1000-grain weight, grain weight per spike and grain number per spike. One locus on chromosome 2B explained 26.3% WUE variation in multiple environments. Under good soil moisture conditions before flowering, the high CID genotype QWue.acn-2BNingchun 27, was associated with WUE, high grain weight per spike, and kilo-grain weight. Under rain-fed conditions, the low CID genotype QWue.acn-2BNingchun 4 tended to maintain more spike number and was associated with improved WUE and yield. The introduction of good chromosome fragments of QWue.acn-2B into elite lines by molecular marker assisted selection will boost up the cultivation of high-yield and water-saving wheat varieties.

Wheat yield is highly correlated with plant height, heading date, spike characteristics, and kernel traits. In this study, we used the wheat55K single nucleotide polymorphism array to genotype a recombinant inbred line population of 165 lines constructed by crossing two tetraploid wheat materials, Icaro and Y4. A genetic linkage map with a total length of 6244.51 cM was constructed, covering 14 chromosomes of tetraploid wheat. QTLs for 12 important agronomic traits, including plant height (PH), heading date (HD), awn color (AC), spike-branching (SB), and related traits of spike and kernel, were mapped in multiple environments, while combined QTL-by-environment interactions and epistatic effects were analyzed for each trait. A total of 52 major or stable QTLs were identified, among which may be some novel loci controlling PH, SB, and kernel length-width ratio (LWR), etc., with LOD values ranging from 2.51 to 54.49, thereby explaining 2.40–66.27% of the phenotypic variation. Based on the ‘China Spring’ and durum wheat reference genome annotations, candidate genes were predicted for four stable QTLs, QPH.nwafu-2B.2 (165.67–166.99 cM), QAC.nwafu-3A.1 (419.89–420.52 cM), QAC.nwafu-4A.1 (424.31–447.4 cM), and QLWR.nwafu-7A.1 (166.66–175.46 cM). Thirty-one QTL clusters and 44 segregation distortion regions were also detected, and 38 and 18 major or stable QTLs were included in these clusters and segregation distortion regions, respectively. These results provide QTLs with breeding application potential in tetraploid wheat that broadens the genetic basis of important agronomic traits such as PH, HD, AC, SB, etc., and benefits wheat breeding.

Grouting is one of the main technical means to prevent water inrush hazards in coal seam floor aquifers. It is of great significance to elucidate the diffusion law of slurry in the process of grouting in fractured aquifers for safe mining in coal mines. In this paper, the mechanism of slurry diffusion in horizontal fractures of fractured aquifers was studied based on the Bingham slurry with time-varying characteristics; additionally, a one-dimensional seepage grouting theoretical model considering the temporal and spatial variation of slurry viscosity under constant grouting rate was established. In this model, the grouting pressure required by the predetermined slurry diffusion radius can be obtained by knowing the grouting hole pressure and injection flow. Slurry properties, fracture parameters, grouting parameters, and water pressure were the parameters affecting the slurry diffusion process. Looking at the problem of water disaster prevention of coal seam floor in the Working Face 2509 of the Chensilou Coal Mine, according to the aquifer parameters and model calculation results, a grouting scheme with a slurry diffusion radius of 20 m and grouting pressure of 12 MPa was proposed. Finally, with the comparative analysis of the transient electromagnetic method (TEM) and water inflow before and after grouting, it was verified that the design grouting pressure and the spacing of grouting holes were reasonable and the grouting effect was good.

In this paper, shear displacement properties of rock fractures were studied, and the energy evolution process was analyzed before sliding instability under complex shear loading paths. The artificial prefabrication method was used to simulate the natural rock fractures, which are difficult to obtain in the natural environment. The prepeak tiered cyclic loading tests under constant normal loading were performed on six rock specimens with fractures by rock direct shear apparatus (RDS-200). To obtain the stress difference of adjacent cycles, the direct shear test was conducted on the other six rock specimens with fractures before the prepeak tiered cyclic shear loading test. The variation trend of residual shear displacement (RSD) and the similarity of loading and unloading curves before slip instability were obtained by analyses of prepeak tiered cyclic shear loading test data. Energy evolution laws of rock fractures were analyzed with the consideration of the hysteresis characteristics, according to the hysteresis effect of shear displacement behind shear stress. This paper provides guidance for the study on shear instability of rock fractures under complex loading paths.

To study the influence of wetting-drying cycles on dynamic mechanical properties of rock masses, the impact compression tests of red sandstone samples were carried out by using a split Hopkinson pressure bar (SHPB) apparatus with a diameter of 50 mm. The results showed that under the same number of wetting-drying cycles, the dynamic compressive strength of red sandstone increased exponentially with the strain rate, and the sensitivity of the strain rate decreased with the increase of wetting-drying cycles. The deterioration effect of wetting-drying cycles was significant, and the dynamic and static compressive strength decreased with the increase of wetting-drying cycles; the higher the strain rate, the stronger the sensitivity to wetting-drying cycles. Besides, the influence of wetting-drying cycles and strain rate was comprehensively studied, and the equation of dynamic compressive strength of red sandstone was obtained. After different wetting-drying cycles, the fractal characteristics of red sandstone dynamic fragmentation were obvious, and the fractal dimension was 2.02–2.80, and the fractal dimension increased logarithmically with the strain rate. Finally, the internal microstructure of red sandstone after different wetting-drying cycles was analyzed, and the degradation mechanism of the rock by the cycles was discussed.

Risk assessment is critical for the construction of the subway station to improve the risk management and reduce the additional loss. According to field investigation of safe construction, the analytical network process (ANP), fuzzy set theory and fuzzy comprehensive evaluation (FCE), a fuzzy ANP comprehensive evaluation (FANPCE) model was proposed to evaluate the risk of subway station construction in this paper. Twelve key risk factors of subway station construction were identified through literature review and questionnaires. The interdependency among risk factors were illustrated through the network structure of ANP, and then a weight matrix of single risk factors was built by comments and survey results, and the interdependent weight matrix was quantified by integrating the triangular fuzzy number into the ANP. Subsequently, the total risk rank of assessed projects can be quantified though the synthesis of weight matrices with the synthetic operator of FCE. Wu Lu Kou subway station was selected as a case study. The results imply that, construction experience, underground water, and safety consciousness have a substantial influence on construction projects and that the total construction risk of Wu Lu Kou subway station is ranked at I level. Moreover, the loss analysis of the whole construction process verifies this method. This research contributes to developing a FANPCE method to identify the risk factors with high weights, assess the risk rank of projects and appropriately respond to the results. In addition, the developed fuzzy set theory-ANP-FCE integrated network provides stakeholders a consolidated model for the risk evaluation.

Tensile strain is one of the main variables that affect fracturing in soil. This paper focuses on an experimental investigation of the deformation characteristics of remolded loess in direct and cyclic tension tests. The material behavior was approximated as elastic-plastic by ignoring the effect of time. In direct tests, the results showed that the change in slope of the stress-strain curve depended on the water content. The plastic constitutive relation was described by two methods. In cyclic loading and unloading tests, the remolded loess exhibited hysteresis (a phase lag), which led to dissipation of the mechanical energy. And no compaction limit phenomenon was found. A simple mathematical model was proposed to predict the plastic cyclic characteristics, and it was validated by the new test data.

Rock engineering is usually associated with impact loads induced by blasting, drilling, vibration, or earthquake. In the engineering fields of tunnelling, slopes, dams, and mining, rocks are always subjected to cyclic wet-dry caused by periodical variation in moisture. To study cyclic wet-dry effects on dynamic compression properties and deterioration of red-sandstone, physical tests and dynamic and static tests were conducted after 0, 5, 10, 15, and 20 wet-dry cycles. Changes in physical and mechanical parameters, including P-wave velocity, density, and static and dynamic compression strength, were determined. Deterioration of red-sandstone caused by wet-dry cycles was verified through physicomechanical parameters, and the microscopic features were scanned by SEM techniques. Experimental results showed that the dynamic compression strength increased with the loading rate, but decreased with the increase of wet-dry cycles. In terms of the loading rate, the decay function model was proposed to evaluate the long-term dynamic compression strength of red-sandstone against cyclic wet-dry action. Besides, the function of the loading rate was obtained. Parameters of two models, decay constant and half-life values, were measured accurately.

Water inrush disasters in mining frequently occur under the influence of confined water-bearing fault zones. Therefore, investigating the fault water inrush mechanism is necessary to reduce the number of occurrences of this type of disaster. In fault zones, the rock is highly fractured, and the mechanism of water conduction is complex. In this research, the seepage mechanism of fractured sandstone in fault zones is studied through experiments, and the results indicate that the permeability coefficient of fractured sandstone depends on the axial stress and particle size. The relationship between the permeability coefficient and axial stress was an exponential relationship. Then, a water-rock coupled model is proposed based on the experimental results, which considers the different water flow patterns during water inrush disasters. Finally, a numerical simulation combined with the water-rock coupled model is conducted to investigate the fault water inrush mechanism of a case study, and the results reveal that when water inrush disasters occur during mining, two types of conditions are required. One is that the connection among the fractured zone of the coal seam roof, fault fracture zone, and aquifer fails, and the other is that the connection among the fractured zone of the water inrush prevention pillar, fault fracture zone, and aquifer fails. This study contributes to an increased understanding of the mechanism of water inrush disasters and the design of water inrush prevention pillars.

The water-blocking properties of the clay layer at the bottom of the Cenozoic overburden in China are an important factor influencing the safety of thin bedrock coal seam mining. Clay has remolding properties that are unlike the nonreversible characteristics of cracks in brittle rock, and failure cracks in clay can reclose or continue to expand under the influence of different external factors. In this work, the soil layer on top of thin bedrock is the research object, and the influences of the particle composition, water content, soil layer thickness, and crack width on the crack development-closure state of soil layer are analyzed by the orthogonal test method. Visual analysis shows that the order of influence of each factor on the stability of soil layer is the crack width, particle composition, soil layer thickness, and water content. The stability of soil layer decreases with increasing crack width and sand content and decreasing soil layer thickness; in addition, soil layer stability decreases first and then increases with increasing water content. Further variance analysis shows that the crack width and particle composition are key factors that impact the stability of soil layer and that the soil layer thickness has some influence, while the water content has little effect on the stability of soil layer. In addition, the crack will reclose when the sand content in soil is less than 50% and the crack width is less than or equal to 1.0 mm, and the soil layer is prone to further failure when the sand content in soil is more than 50% and the crack width is greater than or equal to 3.0 mm; when the soil layer thickness is 15.0 cm, its stability is better than when the soil layer thickness is 10.0 cm or 5.0 cm.

In the engineering fields of mining, tunneling, slopes, and dams, rocks are usually subject to the coupling effect of impact load and wet-dry cycles. The deformation rule of rocks under the coupling effects is a symbolic mechanical property, which lays the foundation for the design and evaluation in the rock engineering. In this paper, the coupling damage was classified as mesodamage induced by wet-dry cycles and macrodamage induced by impact load, and the loading rate effect was considered as the load damage. Besides, a constitutive model of coupling damage was concluded based on Lemaitre’s strain equivalent assumption. Consequently, the validity of the model was verified by a series of dynamic compression tests of red sandstone. Results indicated that the proposed damage constitutive model can definitely describe the dynamic stress-strain curves of red sandstone after wet-dry cycles and impact load. The evolution of coupling damage curves showed that wet-dry cycle damage plays a dominant role in the elastic deformation stage, while the yield failure stage is controlled by the load damage in which the loading rate cannot be ignored. Parametric study was also performed to analyze the effect of parameters on dynamic stress-strain curves. The proposed mode has the simple and reliable operation with few parameters and can efficiently predict the long-term deformation behavior of rocks subject to multiple wet-dry cycles.

Salt stress causes significant reductions in rice production worldwide; thus, improving salt tolerance is a promising approach to meet the increasing food demand. Wild rice germplasm is considered a valuable genetic resource for improving rice cultivars. However, information regarding the improvement of salt tolerance in cultivated rice using wild rice genes is limited. In this study, we identified a salt-tolerant line Dongxiang/Ningjing 15 (DJ15) under salt-stress field conditions from the population of a salt tolerant Dongxiang wild rice × a cultivated rice variety Ningjing16 (NJ16). Genomic resequencing analysis of NJ16, DJ15 and Dongxiang wild rice revealed that the introgressed genomic fragments were unevenly distributed over the 12 chromosomes (Chr.) and mainly identified on Chr. 6, 7, 10, and 11. Using quantitative trait locus (QTL) mapping, we found 9 QTL for salt tolerance (qST) at the seedling stage located on Chr. 1, 3, 4, 5, 6, 8, and 10. In addition, sequence variant analysis within the QTL regions demonstrated that SKC1/HKT8/HKT1;5 and HAK6 transporters along with numerous transcriptional factors were the candidate genes for the salt tolerant QTL. The DJ15/Koshihikari recombinant inbred lines that contained both qST1.2 and qST6, two QTL with the highest effect for salt tolerance, were more tolerant than the parental lines under salt-stress field conditions. Furthermore, the qST6 near-isogenic lines with IR29 background were more tolerant than IR29, indicating that qST1.2 and qST6 could improve salt tolerance in rice. Overall, our study indicates that wild rice genes could markedly improve the salt tolerance of cultivated rice.

Tensile strength is one significant parameter involved in tensile fracture in soil mechanics. In this paper, a stress-controlled, uniaxial, direct-tension test apparatus was developed to investigate the tensile properties of soils. A limited number of investigations have examined the impact of anisotropy and loading interval on the tensile strength of undisturbed loess. The deformation and strains generated were also examined during the tests. It was revealed that anisotropy was an important factor affecting tensile strength of undisturbed loess, and the effect of loading interval on tensile strength significantly depended on water content. It was negligible while the water content was below the plastic limit. However, when the water content was above the plastic limit, the loading interval not only affected the tensile strength, but also the failure displacement and stiffness response of the soil. Two patterns of tensile fracture were summarized and discussed. Moreover, an empirical constitutive relation was proposed to describe the stress-strain relationship of undisturbed loess and its robustness was validated by the experimental data.

The water inrush from karst collapse column (KCC) is a cascading, vicious cycle disaster caused by geological and mining activities, that can cause serious casualties and property losses. The key to preventing this risk is to study the mechanism of water inrush under confining pressure. Aiming at the investigationg the characteristics of the KCC named X1 in Chensilou mine, a series of methods, including connectivity experiments, water pressure monitoring tests in two side-walls, and numerical simulations based on plastic damage-seepage (PD-S) theory have been developed. The methods are used to test the security of the 2519 mining area, the damage thickness, pore water pressure, and seepage vector in the X1. The results indicate that the X1 has a certain water blocking capacity. In addition, with the decrease of confining pressure and increase of shear stress, deviatoric stress could cause the increase of permeability, the reduction of strength, and the reduction of pore water pressure in KCC. Therefore the increased effective stress in the rock will force the rock to become more fractured. Conversely, the broken rock could cause the change of stress, and further initiate new plastic strains, damage and pore water pressure until a new equilibrium is reached. This cascading water inrush mechanism will contribute to the exploitation of deep coal resources in complex geological and hydrogeological conditions.

In order to better understand groundwater influx and protection in coal mining extraction works, an in-house water flow apparatus coupled with an industrial rock testing system, known as MTS 815.02, were used to study the effects of grain size mixtures on the compaction and flow properties of disintegrated, or non-cemented, coal samples. From the Reynolds number evaluation of the samples with different grain mixtures, and the relationship between the water flow velocity and pore pressure gradient differences, it was found that seepage through the mixtures are of non-Darcy flow type. The porosity of coal specimens was found to be highly affected by compaction, and the variations of the porosity were also influenced by the samples’ grain size distribution. It was found that the sample porosity decreases with increasing compaction and decreasing grain sizes. Grain crushing during compaction was observed to be the main cause of the appearance of fine grains, and the washing away of fine grains was consequently the main contributing factor for the weight loss due to water seepage. It was observed that during the tests and with the progression of compaction, permeability k decreases and non-Darcy factor β increases with decreasing porosity φ. The k-φ and β-φ plots show that as the sizes of disintegrated coal samples are getting smaller, there are more fluctuations between the porosity values with their corresponding values of k and β. The permeability value of the sample with smallest grains was observed to be considerably lower than that of the sample with largest grains. Non-Darcy behavior could reduce the hydraulic conductivity. It was found that the porosity, grain breakage and hydraulic properties of coal samples are related to grain sizes and compaction levels, as well as to the arrangement of the grains. At high compaction levels, the porosity of disintegrated coal samples decreased strongly, resulting in a significant decrease of the permeability at its full compression state; Non-Darcy flow behavior has the slightest effect in uniform samples, therefore, indicating that disintegrated coal in uniform grain size mixtures could be treated as an aquicluding (water-resisting) stratum.

The Hippo pathway effector Yes-associated protein (YAP) regulates liver size by promoting cell proliferation and inhibiting apoptosis. However, recent in vivo studies suggest that YAP has important cellular functions other than controlling proliferation and apoptosis. Transgenic YAP expression in mouse hepatocytes results in severe jaundice. A possible explanation for the jaundice could be defects in adherens junctions that prevent bile from leaking into the blood stream. Indeed, immunostaining of E-cadherin and electron microscopic examination of bile canaliculi of Yap transgenic livers revealed abnormal adherens junction structures. Using primary hepatocytes from Yap transgenic livers and Yap knockout livers, we found that YAP antagonizes E-cadherin-mediated cell-cell junction assembly by regulating the cellular actin architecture, including its mechanical properties (elasticity and cortical tension). Mechanistically, we found that YAP promoted contractile actin structure formation by upregulating nonmuscle myosin light chain expression and cellular ATP generation. Thus, by modulating actomyosin organization, YAP may influence many actomyosin-dependent cellular characteristics, including adhesion, membrane protrusion, spreading, morphology, and cortical tension and elasticity, which in turn determine cell differentiation and tissue morphogenesis. [ABSTRACT FROM AUTHOR]

A shape memory alloy (SMA)-wire actuated release actuator with an extremely long lifetime was designed and validated. To ensure the ability of repeated actuation, two stages of ball-lock mechanisms were adopted to reduce the load in the SMA wire. In addition, a length-increasing design of the SMA wire was employed. Validation tests, including function tests, vibration tests, shock tests, and thermal vacuum tests were conducted on prototypes. According to the test results, the actuator can release a maximum preload of 15 kN and has a lifetime of more than 693 cycles. Furthermore, the actuator can function well, even under severe thermal and vibration environments. [ABSTRACT FROM AUTHOR]

Escherichia coli MutY is an adenine and weak guanine DNA glycosylase involved in reducing the mutagenic effects of 7,8-dihydro-8-oxoguanine (GO). MutY contains three structural domains: an iron-sulfur module, a six-helix barrel module with the helix-hairpin-helix motif, and a C-terminal domain. Here, we demonstrate that the mutant MutY(Δ26-134), which lacks the six-helix barrel domain, cannot complement the mutator phenotype of a mutY mutant in vivo. However, the mutant can still bind DNA and has weak catalytic activity at high enzyme concentrations. The mutant is a dimer in solution and assembled into two and multiple (up to five) complexes with 20- and 44-bp DNA fragments, respectively, in a concentration-dependent manner. Higher order complexes with DNA substrates containing A/GO mismatches were formed at lower protein concentrations than with the A/G mismatch and homoduplex DNA. Measurement of equilibrium binding using fluorescence anisotropy showed that the mutant protein retains some specificity for A/GO-containing DNA substrates and that the binding event is highly cooperative. This is consistent with the MutY structure determined, which indicates that GO specificity is contributed by both the six-helix barrel and C-terminal domains. The nonspecific binding of MutY(Δ26-134) to DNA suggests a model in which the specific binding of mismatched DNA by MutY involves sequential interactions, in which one MutY molecule scans the DNA and enhances binding of another MutY molecule to the A/GO mismatch. [ABSTRACT FROM AUTHOR]

Escherichia coli MutY and MutS increase replication fidelity by removing adenines that were misincorporated opposite 7,8-dihydro-8-oxo-deoxyguanines (8-oxoG), G, or C. MutY DNA glycosylase removes adenines from these mismatches through a short-patch base excision repair pathway and thus prevents G:C-to-T:A and A:T-to-G:C mutations. MutS binds to the mismatches and initiates the long-patch mismatch repair on daughter DNA strands. We have previously reported that the human MutY homolog (hMYH) physically and functionally interacts with the human MutS homolog, hMutSα (Y. Gu et al., J. Biol. Chem. 277:11135-11142, 2002). Here, we show that a similar relationship between MutY and MutS exists in E. coli. The interaction of MutY and MutS involves the Fe-S domain of MutY and the ATPase domain of MutS. MutS, in eightfold molar excess over MutY, can enhance the binding activity of MutY with an A/8-oxoG mismatch by eightfold. The MutY expression level and activity in mutS mutant strains are sixfold and twofold greater, respectively, than those for the wild-type cells. The frequency of A:T-to-G:C mutations is reduced by two- to threefold in a mutS mutY mutant compared to a mutS mutant. Our results suggest that MutY base excision repair and mismatch repair defend against the mutagenic effect of 8-oxoG lesions in a cooperative manner. [ABSTRACT FROM AUTHOR]