Emerging roles of DNA-PK besides DNA repair

The DNA-dependent protein kinase (DNA-PK) is a DNA-activated serine/threonine protein kinase, and abundantly expressed in almost all mammalian cells. The roles of DNA-PK in DNA-damage repair pathways, including non-homologous end-joining (NHEJ) repair and homologous recombinant (HR) repair, have been studied intensively. However, the high levels of DNA-PK in human cells are somewhat paradoxical in that it does not impart any increased ability to repair DNA damage. If DNA-PK essentially exceeds the demand for DNA damage repair, why do human cells universally express such high levels of this huge complex? DNA-PK has been recently reported to be involved in metabolic gene regulation in response to feeding/insulin stimulation; our studies have also suggested a role of DNA-PK in the regulation of the homeostasis of cell proliferation. These novel findings expand our horizons about the importance of DNA-PK.     

紫外辐射诱导植物叶片DNA损伤敏感性差异

单细胞凝胶电泳（彗星检测,cometassay）技术已广泛应用于动物细胞DNA损伤检测,但在植物细胞DNA损伤检测中的应用尚不多见。本研究通过对动物细胞彗星检测方法的改进,利用植物细胞原生质体作为材料,研究了不同发育期九里香（Murraya panicuata）叶片对UV-B诱导的DNA损伤的敏感性差异。彗星检测结果表明,九里香叶片DNA的损伤程度与UV-B辐射的剂量呈正相关：在相同UV—B辐射剂量下,九里香幼嫩叶片比成熟叶片的DNA损伤量大,表明其幼嫩叶片对UV-B辐射的敏感性比成熟叶片高。     

羊草和大针茅群落的暗呼吸强度与环境条件关系的初步探讨

草原群落的干物质产量,是由光合作用和呼吸作用所决定。呼吸作用对于干物质的生产是必不可少的一环,因为任何物质的形成都需要能量,而这种能量正是由呼吸作用所提供的。#br#草原群落的生长、呼吸和光合受到光照、温度、水分和土肥等环境因子的影响。在适宜的气候条件下,生长、呼吸和光合有着严格的偶联关系,并能使群落的生长效率保持比较高的水平,然而在异常的气候条件下,如高温、干旱、低湿等,会增加群落的无效呼吸,使光合产物过量的消耗,导致偶联关系的破坏,光合效率下降,终致造成植物的死亡。#br#本文就羊草和大针茅草原群落的暗呼吸强度与环境条件的关系进行探讨,视其对草原群落光合生产效率的影响,从而为人工促进天然草原生产力的提高,提供依据。     

Polyhydroxybutyrate production from lactate using a mixed microbial culture

In this study we investigated the use of lactate and a lactate/acetate mixture for enrichment of poly-3-hydroxybutyrate (PHB) producing mixed cultures. The mixed cultures were enriched in sequencing batch reactors (SBR) that established a feast-famine regime. The SBRs were operated under conditions that were previously shown to enable enrichment of a superior PHB producing strain on acetate (i.e., 12 h cycle length, 1 day SRT and 30°C). Two new mixed cultures were eventually enriched from activated sludge. The mixed culture enriched on lactate was dominated by a novel gammaproteobacterium. This enrichment can accumulate over 90 wt% PHB within 6 h, which is currently the best result reported for a bacterial culture in terms of the final PHB content and the biomass specific PHB production rate. The second mixed culture enriched on a mixture of acetate and lactate can produce up to 84 wt% PHB in just over 8 h. The predominant bacterial species in this culture were Plasticicumulans acidivorans and Thauera selenatis, which have both been reported to accumulate large amounts of PHB. The data suggest that P. acidivorans is a specialist on acetate conversion, whereas Thauera sp. is a specialist on lactate conversion. The main conclusion of this work is that the use of different substrates has a direct impact on microbial composition, but has no significant effect on the functionality of PHB production process.     

Comparative study on calli from two reed ecotypes under heat stress

The different physiological responses to heat stress in calli from two ecotypes of common reed (Phragmites communis Trin.) plants (dune reed (DR) and swamp reed (SR)) were studied. The relative water content, the relative growth rate, cell viability, membrane permeability (MP), H₂O₂ content, MDA content, proline level, and the activities of enzymes, such as superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), ascorbate peroxidase (APX), glutathione reductase (GR), and lipoxygenase (LOX) were assayed. Results showed that under heat stress, DR callus could maintain the higher relative growth rate and cell viability than SR callus, while H₂O₂ content, MDA content, and MP in SR callus increased more than in DR callus. The activities of antioxidant enzymes, such as SOD, CAT, POD, APX, and GR in two calli were enhanced by high temperature. However, antioxidant enzymes in DR callus showed the higher thermal stability than those in SR callus. LOX activity increased more in SR callus than in DR callus under heat stress. High temperature markedly elevated proline content in DR callus whereas had no effect on that in SR callus. Taken together, DR callus is more thermotolerant than SR callus, which might be due to the higher activity of antioxidant enzymes and proline level compared with SR callus under heat stress.     

DNA组装新方法的研究进展

2010年,蕈状支原体Mycoplasma mycoides的人工合成,迎来了合成生物学的崭新时代.这种突破性的进展主要得益于酵母自身强大的DNA体内重组能力.近几年来,除了利用体内重组的DNA大片段拼接技术,基于连接或聚合思想的不同尺度的DNA体外组装方法也相继出现,如Biobrick\Bglbrick、SLIC与Gibson等温一步法等,这些方法的应用加快了合成生物学功能元件库、生物合成途径乃至微生物染色体的人工构建.事实上,目前所建立的各种DNA组装方法,均是由DNA分子拼接理念(包括两分子衔接思想与多片段组装模式)衍生而来.文中将在介绍DNA组装基本理念的基础上,对体内、体外主要的DNA组装方法进行简要梳理,希望为不同类型的合成生物学功能器件及生物合成途径的构造提供参考与借鉴.     

杂交水稻谷粒性状三种不育胞质遗传效应的分析

利用K型、D型和W型三种不育胞质与三个保持系培育成的9个（三套）同质异核或同核异质不育系,以其与5个恢复系按p×q交配模式设计,研究三种不育胞质对F1粒长、粒宽、千粒重和长／宽等谷粒性状的遗传效应．结果表明：各性状均以不育胞质一般配合力效应最重要,随性状而异,还有与保持系、恢复系及二者的一、二级特殊配合力效应;三种不育胞质各性状的一般配合力效应均表现显著或极显著差异,K胞质在千粒重方面、D胞质在粒长和长／宽方面、W胞质在粒宽方面有加性促进作用．因此,注意选择不育胞质源和对质核组合的评价,可进一步改良杂交水稻谷粒性状.     

A 3-hydroxy-3-methylglutaryl-CoA synthase-based probe for the discovery of the acyltransferase-less type I polyketide synthases

Acyltransferase (AT)-less type I polyketide synthases (PKSs) produce complex natural products due to the presence of many unique tailoring enzymes. The 3-hydroxy-3-methylglutaryl coenzyme A synthases (HCSs) are responsible for β-alkylation of the growing polyketide intermediates in AT-less type I PKSs. In this study, we discovered a large group of HCSs, closely associated with the characterized and orphan AT-less type I PKSs through in silico genome mining, sequence and genome neighbourhood network analyses. Using HCS-based probes, the survey of 1207 in-house strains and 18 soil samples from different geographic locations revealed the vast diversity of HCS-containing AT-less type I PKSs. The presence of HCSs in many AT-less type I PKSs suggests their co-evolutionary relationship. This study provides a new probe to study the abundance and diversity of AT-less type I PKSs in the environment and microbial strain collections. Our study should inspire future efforts to discover new polyketide natural products from AT-less type I PKSs.     

Interaction with Tap42 is required for the essential function of Sit4 and type 2A phosphatases

In Saccharomyces cerevisiae, Pph21 and Pph22 are the two catalytic subunits of type 2A phosphatase (PP2Ac), and Sit4 is a major form of 2A-like phosphatase. The function of these phosphatases requires their association with different regulatory subunits. In addition to the conventional regulatory subunits, namely, the A and B subunits for Pph21/22 and the Sap proteins for Sit4, these phosphatases have been found to associate with a protein termed Tap42. In this study, we demonstrated that Sit4 and PP2Ac interact with Tap42 via an N-terminal domain that is conserved in all type 2A and 2A-like phosphatases. We found that the Sit4 phosphatase in the sit4-102 strain contains a reverse-of-charge amino acid substitution within its Tap42 binding domain and is defective for formation of the Tap42-Sit4 complex. Our results suggest that the interaction with Tap42 is required for the activity as well as for the essential function of Sit4 and PP2Ac. In addition, we showed that Tap42 is able to interact with two other 2A-like phosphatases, Pph3 and Ppg1.