ATP binding and hydrolysis by Saccharomyces cerevisiae Msh2–Msh3 are differentially modulated by mismatch and double-strand break repair DNA substrates

In Saccharomyces cerevisiae, Msh2–Msh3-mediated mismatch repair (MMR) recognizes and targets insertion/deletion loops for repair. Msh2–Msh3 is also required for 3′ non-homologous tail removal (3′NHTR) in double-strand break repair. In both pathways, Msh2–Msh3 binds double-strand/single-strand junctions and initiates repair in an ATP-dependent manner. However, we recently demonstrated that the two pathways have distinct requirements with respect to Msh2–Msh3 activities. We identified a set of aromatic residues in the nucleotide binding pocket (FLY motif) of Msh3 that, when mutated, disrupted MMR, but left 3′NHTR largely intact. One of these mutations, msh3Y942A, was predicted to disrupt the nucleotide sandwich and allow altered positioning of ATP within the pocket. To develop a mechanistic understanding of the differential requirements for ATP binding and/or hydrolysis in the two pathways, we characterized Msh2–Msh3 and Msh2–msh3Y942A ATP binding and hydrolysis activities in the presence of MMR and 3′NHTR DNA substrates. We observed distinct, substrate-dependent ATP hydrolysis and nucleotide turnover by Msh2–Msh3, indicating that the MMR and 3′NHTR DNA substrates differentially modify the ATP binding/hydrolysis activities of Msh2–Msh3. Msh2–msh3Y942A retained the ability to bind DNA and ATP but exhibited altered ATP hydrolysis and nucleotide turnover. We propose that both ATP and structure-specific repair substrates cooperate to direct Msh2–Msh3-mediated repair and suggest an explanation for the msh3Y942A separation-of-function phenotype.     

填充床反应器中酶法连续合成甘油二酯的研究

近年来,1,3-甘油二酯(DAG)由于其广泛用途及健康作用日益受到人们的重视。报道了一种无溶剂条件下填充床反应器中连续酶促合成1,3-DAG的方法。研究了填充柱的长径比、进料体积流速、温度、底物摩尔比对酯化率和1,3-DAG产量的影响。结果表明固定化酶填充柱长径比7.8,亚油酸、甘油摩尔比1∶2 ,进料速度1.2mL/min ,65℃条件下酯化反应可实现脂肪酸酯化率、1,3-DAG纯度及生产效率的统一。填充床反应器中固定化酶连续催化酯化反应的一个主要问题即体系水分清除困难。实验研究了采用过量甘油吸附脱水的可行性,亚油酸、甘油摩尔比为1∶2时,可明显改善固定化酶的稳定性,增加LipozymeRMIM的使用寿命。连续运行10d ,残余酶活仍保持在80 %以上,而对照组则仅为52%。     

限氧自养硝化-反硝化生物脱氮新技术

限氧自养硝化—反硝化是部分硝化与厌氧氨氧化相耦联的生物脱氮反应过程,通过严格控制溶解氧在0．1～0．3mg·L^-1,实现硝化反应控制在亚硝酸阶段,然后以硝化阶段剩余的NH4^+作为电子供体,在厌氧条件下实现反硝化,该反应过程是完全的自养硝化—反硝化过程,具有能耗低、脱氮效率高、反应系统占地面积小等优点,适用于处理COD／NH4^+—N低的废水,是一种非常有应用前景的生物脱氮技术,文中详细介绍了限氧自养硝化—反硝化生物脱氮反应过程的研究进展,讨论了其微生物学机理及应用前景。     

Serological tests for COVID-19: Potential opportunities

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a novel betacoronavirus, caused a pandemic leading to a standstill of nearly all global activities. There are some controversies on the production of specific immunoglobulin M (IgM) and IgG antibodies after the infection with SARS-CoV-2. This paper seeks to elaborate on the potential application of IgM and IgG antibodies and the viral antigens for the diagnosis and the course of the disease as well as the recurrence of positive nucleic acid tests after discharge.     

A Method for Making Aceto-Carmin Smears Permanent

Anthers are collected and placed in a solution of 1 part acetic acid to 3 parts of absolute alcohol. The contents of the anther are squeezed out on a slide in a drop of Belling's iron-aceto-carmin solution and a cover glass placed over the drop. Care should be taken to remove all anther walls and flower parts. Heat the slide over an alcohol flame for a second, repeating 4 or 5 times. Place the slide in a petri dish filled with a 10% solution of acetic acid. When the cover glass has risen away from the slide gently remove the cover glass and place in a Coplin jar containing equal parts of alcohol and acetic acid. Likewise, place the slide in this solution. Run both cover and slide thru the following solutions: 1 part acetic acid to 3 parts absolute alcohol, 1 part acetic acid to 9 parts absolute alcohol, absolute alcohol and finally equal parts of absolute alcohol and xylol. Recombine the cover and slide in xylol-balsam directly from this solution.     

The differential contributions of herkogamy and dichogamy as mechanisms of avoiding self‐interference in four self‐incompatible Epimedium species

Self‐interference is one of the most important selective forces in shaping floral evolution. Herkogamy and dichogamy both can achieve reductions in the extent of self‐interference, but they may have different roles in minimizing self‐interference in a single species. We used four self‐incompatible Epimedium species to explore the roles of herkogamy and dichogamy in avoiding self‐interference and to test the hypothesis that herkogamy and dichogamy may be separated and become selected preferentially in the taxa. Two species (E. franchetii and E. mikinorii) expressed strong herkogamy and weak protogyny (adichogamy), whereas another two species (E. sutchuenense and E. leptorrhizum) expressed slight herkogamy and partial protandry. Field investigations indicated that there was no physical self‐interference between male function and female function regarding pollen removal and pollen deposition in all species. Self‐pollination (autonomous or facilitated) was greater in species with slight herkogamy than in those with strong herkogamy. Artificial pollination treatments revealed that self‐pollination could reduce outcrossed female fertility in all species, and we found evidence that self‐interference reduced seed set in E. sutchuenense and E. leptorrhizum in the field, but not in E. franchetii and E. mikinorii. These results indicate that well‐developed herkogamy is more effective compared with dichogamy in avoiding self‐interference in the four species. In genus Epimedium, herkogamy instead of dichogamy should be selected preferentially and evolved as an effective mechanism for avoiding self‐interference and might not need to evolve linked with dichogamy.     

The CQ ratio of surface energy components influences adhesion and removal of fouling bacteria

The interaction energy between bacteria and substrata with different surface energies was modelled by the extended DLVO (Derjaguin, Landau, Verwey and Overbeek) theory. The modeling results revealed that the interaction energy has a strong correlation with the CQ (Chen and Qi) ratio, which is defined as the ratio of the Lifshitz–van der Waals (LW) apolar to the electron donor surface energy components of substrata. Both modeling and experimental results with different bacteria including P. fluorescens, Cobetia marina and Vibrio alginolyticus demonstrated that if the LW surface energy of bacteria is larger than that of water, which is the case for most bacteria, the number of adhered bacteria decreases with a decreasing CQ ratio while bacterial removal rate increases with a decreasing CQ ratio. However, if the LW surface energy of bacteria is less than that of water, the opposite results are obtained. The CQ ratio gives a clear direction for the design of anti-biofouling and biofouling-release coatings through surface modification.     

Effect of Carbohydrates and Starvation on Nitrogen Sparing Action of Methionine and Threonine in Rats

Formaldehyde dehydrogenase from Pseudomonas putida C-83 was found to contain 7 halfcystine residues per subunit monomer, as checked by the method of performic acid oxidation. Approximately 7 sulfhydryl groups per subunit monomer were titrated with 5,5′-dithiobis(2-nitrobenzoic acid) (DTNB) after denaturation with 8 m urea. In the native enzyme, modification of three sulfhydryl groups per subunit with p-chloromercuribenzoate (PCMB) led to the complete loss of enzyme actiyities for both formaldehyde and n-butanol. Hydrogen-peroxide competitively inhibited the enzyme activity for formaldehyde, while it was only slightly inhibitory to the activity for n-butanol. Both formaldehyde and hydrogen-peroxide protected one sulfhydryl group per subunit monomer from modification with PCMB. Moreover, hydrogen-peroxide was hardly reactive to the enzyme which was preincubated with formaldehyde.

From these observations, we conclude that one of three PCMB-reactive sulfhydryl groups is essential for the binding of formaldehyde, and hydrogen-peroxide modifies this sulfhydryl group.