前体mRNA剪接及剪接调节因子SR蛋白和Tra2蛋白

在高等真核生物中,前体mRNA的剪接及其调节是一个复杂的、由多因子参与的过程,它对基因的正常功能的发挥起着重要的作用,任何一种剪接调节因子的异常变化均有可能导致疾病的发生。因此,研究参与前体mRNA剪接调控的相关因子的功能及作用机制,对前体mRNA剪接机制的阐明,无疑是相当必要的。本文着重介绍了两类重要的mRNA剪接调节蛋白——SR蛋白和Tra2蛋白的研究近况,以期对前体mRNA剪接机制的研究的重要性和复杂性有更多的了解。     

SR蛋白家族在RNA剪接中的调控作用

SR蛋白家族成员都具有一个富含丝氨酸/精氨酸(S/R)重复序列的RS结构域,在RNA剪接体的组装和选择性剪接的调控过程中具有重要的作用。绝大多数SR蛋白是生存的必需因子,通过其RS结构域和特有的其他结构域,实现与前体mRNA的特异性序列或其他剪接因子的相互作用,协同完成剪接位点的正确选择或促进剪接体的形成。深入研究SR蛋白家族在RNA选择性剪接中的调控机制,可以促进以疾病治疗或害虫防治为目的的应用研究。该文总结了SR蛋白家族在基础研究和应用方面的进展。     

钙调蛋白在植物发育中的功能

钙调蛋白(CaM)在植物生长和发育中有着多种功能,它参与了一系列的发育过程如细胞分裂、细胞代谢、胁迫、花药和雌蕊以及胚胎的发育等．对钙调蛋白功能的了解将有助于更深入研究钙/钙调蛋白介导的信号网络,为研究植物体内各类代谢的信号转导奠定基础．     

桥粒相关蛋白Pinin的生物学功能及其在肿瘤发生中的作用

桥粒不但参与上皮和心肌细胞的连接,增强细胞承受机械应力时的黏附作用,还能调控细胞行为和组织形态发生改变时的信号传导通路过程.桥粒相关蛋白Pinin(PNN)自发现以来,其位置和功能就备受争议.现有结果表明,PNN包含与细胞膜上桥粒共定位的桥粒型PNN和位于细胞核中的核型PNN两种,前者参与上皮细胞的黏附,后者与m RNA的选择性剪接功能有关.新近研究发现,PNN与肿瘤发生密切相关,然而其作用及其分子机制却不相同.本文对PNN的结构、功能及其与肿瘤发生的关系作一综述.     

mRNA选择性剪切在植物发育中的作用

mRNA选择性剪切（altemativesplicing）是生物体基因转录调控的基本方式之一,随着新一代测序技术的广泛应用,越来越多的基因的选择性剪切现象被揭示。在植物发育的不同阶段及其应对外界逆境胁迫的过程中,许多基因发生了选择性剪切,产生植物各个发育阶段所需的特定蛋白质来完成不同的发育过程和形成不同应答因子以适应外界环境的变化。本文从种子发育、器官形态发育、开花时间、生物钟调控、环境胁迫等方面综述选择性剪切在植物发育中的研究进展。     

Prp8蛋白在前体mRNA剪接中的作用

前体mRNA的剪接是基因表达的关键一步,发生在蛋白质的转录之后与合成之前.在前体mRNA剪接加工过程中需要将转录本中的内含子切除,因为它会干扰基因的转录.前体mRNA的剪接发生在细胞核中,是在一个大的RNA与蛋白质的复合物即剪接体的催化下完成的.Prp8 （precursor mRNA processing）是参与前体mRNA剪接的最大的蛋白,其序列从酵母到人类是高度保守的.Prp8同时也是细胞核内一个最重要的剪接因子.在剪接过程中,Prp8组成剪接体的催化中心.有人推断Prp8是剪接体的支架蛋白,很可能在催化中心起到锚定RNA的作用,同时也调节着激活剪接体所必需的构象变化.Prp8还与色素性视网膜炎的发生密切相关.     

热激蛋白90在植物发育和疾病抗性中的作用

相对分子质量90000的热激蛋白（heatshock protein,HSP90）是真核细胞必需的分子伴侣。拟南芥中HSP90有7个成员,其中AtHSP90-1、AtHSP90-2、AtHSP90-3和AtHSP90-4组成细胞质亚族;AtHSP90-5、AtHSP90-6、AtHSP90-7分别位于叶绿体、线粒体和内质网。HSP90分子伴侣复合物在植物发育和对外部刺激应答中非常重要,尤其是在抗性（resistance R）蛋白介导的抵抗病毒侵入的过程中起重要作用。     

植物microRNAs在植物发育和非生物胁迫响应中的作用

microRNAs(miRNAs)是一类内源的长度约为22个核苷酸的非编码小分子RNA,其通过对靶基因mRNA进行切割或翻译抑制调节mRNA的表达,在植物中起到重要的作用.主要介绍了植物miRNAs的特征、合成和作用机制,综述了miRNAs在植物生长发育和非生物胁迫响应中的作用.     

mRNA差别显示技术在植物发育研究中的应用

mRNA差别显示技术是近年发展起来的研究基因表达差异的有效方法。它不仅可比较基因表达差异、追踪已知基因的表达情况,而且可作为寻找特异表达基因的重要手段。本文介绍此方法在植物春化作用、光周期反应、花发育、雄性不育、成熟、衰老、种子发育和休眠及根发育等研究领域的应用概况。     

PPR蛋白在植物生长发育中的作用

PPR蛋白在陆生植物中属于最大的蛋白家族之一,其成员种类和数量均十分庞大。PPR蛋白主要的功能是通过在多种细胞器中进行定位从而参与细胞核和细胞器中特异单链RNA的转录后修饰和编辑,在植物生长发育的多个阶段均发挥着重要的作用。多数PPR蛋白编码基因的突变体呈现异常的发育表型,如胚胎致死、发育迟缓及绿化延迟等。对近年来植物PPR蛋白的分类、定位、RNA修饰的机制及其对植物生长发育影响进行了综述,并展望了植物PPR发挥功能区域和参与的调控网络研究。     

Phosphorylation Drives a Dynamic Switch in Serine/Arginine-Rich Proteins

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多聚腺苷酸结合蛋白的结构与功能

多聚腺苷酸结合蛋白[poly（A）-binding protein,PABP]是一类可以与mRNA 3′端Poly（A）结合的高度保守的蛋白质,可通过与Poly（A）的结合参与mRNA的翻译并调节其稳定性。PABP在脊椎动物配子发生和早期胚胎聋亨中也发挥重要的作用。PABP成员还在不断的发现之中,不同类型的细胞中具有结构和功能各异的Poly（A）结合蛋白。     

钙/钙调蛋白依赖性丝氨酸蛋白激酶的结构和功能

钙/钙调蛋白依赖性丝氨酸蛋白激酶(calcium/calmodulin-dependent serine protein kinase, CASK)属于膜相关鸟苷酸激酶（membrane associated guanylate kinase, MAGUK）家族.CASK具有多个不同蛋白质结合结构域，在细胞膜的特定区域，与其他蛋白质形成多种蛋白质复合体，参与组成细胞骨架.它通过衔接细胞外信号蛋白和细胞内骨架蛋白，协助功能蛋白质的转运和定位，以及细胞内的信号传递.此外CASK还可以进入细胞核影响基因转录调控，以及作用在神经突触膜上参与神经递质的释放.     

14-3-3蛋白对植物发育的调控作用

14-3-3蛋白是高度保守并在真核生物中普遍存在的一类调节蛋白。不同的14-3-3蛋白同工型具有不同的细胞特异性, 并通过识别特异的磷酸化序列与靶蛋白相互作用, 被称为蛋白质与蛋白质相互作用的桥梁蛋白。在植物生长发育过程中, 14-3-3蛋白通过与其它蛋白的相互作用参与多种植物激素信号转导、各种代谢调控、物质运输和光信号应答等调控过程。该文主要对近年来有关14-3-3蛋白在植物生长发育中的调控作用, 特别是14-3-3蛋白参与调控植物激素信号转导等方面的研究进展进行综述。     

Roles of Periplasmic Chaperone Proteins in the Biogenesis of Serine Protease Autotransporters of Enterobacteriaceae

The serine protease autotransporters of Enterobacteriaceae (SPATEs) represent a large family of virulence factors. The prevailing model for autotransporter secretion comprises entry to the periplasm via the Sec apparatus, followed by an obscure series of steps in which the C terminus of the periplasmic species inserts into the outer membrane as a β-barrel protein, accompanied by translocation of the passenger domain to the bacterial cell surface. Little is known about the fate of the autotransporter proteins in the periplasm, including whether accessory periplasmic proteins are involved in translocation to the external milieu. Here we studied the role of the major periplasmic chaperones in the biogenesis of EspP, a prototype SPATE protein produced by Escherichia coli O157:H7. The yeast two-hybrid approach, secretion analysis of chaperone mutant strains, and surface plasmon resonance analysis (SPR) revealed direct protein-protein interactions between the periplasmic SurA and DegP chaperones and either the EspP-β or EspP passenger domains. The secretion of EspP was moderately reduced in the surA and skp mutant strains but severely impaired in the degP background. Site-directed mutagenesis of highly conserved aromatic amino acid residues in the SPATE family resulted in ∼80% reduction of EspP secretion. Synthetic peptides containing aromatic residues derived from the EspP passenger domain blocked DegP and SurA binding to the passenger domain. SPR suggested direct protein-protein interaction between periplasmic chaperones and the unfolded EspP passenger domain. Our data suggest that translocation of AT proteins may require accessory factors, calling into question the moniker “autotransporter.”Secretion of proteins to the surface of gram-negative bacteria requires passage through the inner membrane (IM), the periplasm, and the outer membrane (OM). This formidable series of obstacles can be overcome only by complex biological processes. The autotransporter (AT) system, probably the most common gram-negative secretion mechanism (13), is characterized by formation of an OM β-barrel comprised of the C terminus of the periplasmic species. The precise events required for AT translocation across the OM, however, are controversial. The original model for OM translocation comprised targeting to the periplasm via the Sec apparatus, followed by formation of an OM β-barrel, which mediates passage of an unfolded or partially folded N-terminal passenger domain to the extracellular milieu (30). Three models of AT translocation have gained some acceptance (3, 16). According to the hairpin model, translocation of the passenger domain is initiated with the C-terminal end of the passenger forming a hairpin structure inside the AT β-barrel, followed by movement of the rest of the passenger through the barrel''s pore in a C-to-N direction. Under the Omp85 model, the pore-forming Omp85 (YaeT in Escherichia coli) OM protein (OMP) facilitates insertion of the AT translocator domain into the OM, whereupon the AT passenger domain translocates through the Omp85 pore. A third model entails the combination of the hairpin and Omp85 models, including concerted insertion and translocation. All models must reconcile observations seemingly in conflict. Bernstein and colleagues reported cleavage of the mature passenger by a protease located inside the C-terminal AT barrel (10); yet, the dimensions of the folded AT barrel channel are by most accounts too narrow to accommodate even a partially folded passenger species, which is suggested from experimental periplasmic disulfide bond formation within the passenger domain (7, 19, 21).The term “autotransporter” was initially proposed on the assumption that the translocated species contained all necessary information for movement to the extracellular space. We and others have challenged that assumption (11, 14). Recently, several periplasmic proteins have been implicated in the targeting and assembly of extracytoplasmic proteins, principally OMPs (27). Three biological functions have been recognized for these periplasmic proteins: (i) molecular chaperones such as DegP, SurA, Skp, FkpA, PpiA, and PpiD (1, 5, 8, 9, 23, 26) stabilize nonnative conformations of target proteins and facilitate their folding; (ii) peptidyl-prolyl cis-trans isomerases, such as SurA, PpiD, and FkpA (9, 33, 36), catalyze the rate-limiting steps of isomerization during folding; and (iii) proteases, such as DegP and DegQ (22), degrade unproductive or misfolded proteins. Recent reports have suggested the involvement of chaperones during the passage of the AT through the periplasm (31, 43), although the mechanisms have not been defined.Here we demonstrate further the requirement for periplasmic chaperones in the biogenesis of the serine protease ATs of Enterobacteriaceae (SPATEs). Our data suggest a requirement for these periplasmic factors in translocation and suggest direct binding of the chaperone proteins to specific highly conserved motifs in the AT passenger and β-domains.     

植物光合产物转运蛋白及其生物学功能

文章就高等植物光合同化物转运蛋白家族的结构、分类、表达位点、生物学功能及其与光合同化物运输和分配的关系的研究进展作介绍。