几种内源性小RNA的比较

RNA干涉是近年来的研究热点,广泛参与生物发育、细胞分化、细胞凋亡等多种生物学过程。本文综述了近年来对转录后靶基因调控的几种小RNA：siRNA、microRNA、piRNA和endo-siRNA,从特点、生物发生过程和生物学功能方面进行了综述性地比较,以期为进一步深入研究提供参考。     

A new secreted protein that binds to Wnt proteins and inhibits their activities

The Wnt proteins constitute a large family of extracellular signalling molecules that are found throughout the animal kingdom and are important for a wide variety of normal and pathological developmental processes. Here we describe Wnt-inhibitory factor-1 (WIF-1), a secreted protein that binds to Wnt proteins and inhibits their activities. WIF-1 is present in fish, amphibia and mammals, and is expressed during Xenopus and zebrafish development in a complex pattern that includes paraxial presomitic mesoderm, notochord, branchial arches and neural crest derivatives. We use Xenopus embryos to show that WIF-1 overexpression affects somitogenesis (the generation of trunk mesoderm segments), in agreement with its normal expression in paraxial mesoderm. In vitro, WIF-1 binds to Drosophila Wingless and Xenopus Wnt8 produced by Drosophila S2 cells. Together with earlier results obtained with the secreted Frizzled-related proteins, our results indicate that Wnt proteins interact with structurally diverse extracellular inhibitors, presumably to fine-tune the spatial and temporal patterns of Wnt activity.     

Intracellular transport of microinjected 5S and small nuclear RNAs

The mechanism by which some RNAs are segregated in the cell nucleus was analysed by microinjecting 32 P-labelled total RNA from HeLa cells into the cytoplasm of Xenopus oocytes. Small nuclear RNAs (u1, U2, U4, U5 and U6) migrated into the cell nucleus, where they became 30-60 fold more concentrated than in the cytoplasm. Other RNAs, such as tRNA and 7S RNA, remained in the cytoplasm, while 5S RNA became concentrated in the nucleolus. Studies with lupus erythematosus antibodies showed that the migrating RNAs become associated with oocyte RNA-binding proteins.     

A consensus amino-acid sequence repeat in Torpedo and mammalian Ca2+-dependent membrane-binding proteins

A group of calcium-binding proteins which bind to biomembranes has recently been identified in widely different cells and tissues (refs 1-7, reviewed in ref. 8). Three of these proteins (p70, p36 and p32.5) cross-react with antiserum to calelectrin, a Ca2+-binding protein (relative molecular mass 34,000 (34K] from the ray Torpedo marmorata, giving rise to their designation as calelectrin-related proteins. We now report that calelectrin, p36 and p32.5 contain a 17-amino-acid consensus sequence which is conserved and present in multiple copies. We suggest that this sequence may be common to other members of this new group of Ca2+-binding proteins and may underlie their unusual mode of combination with biomembranes.     

Structural basis for 5'-end-specific recognition of guide RNA by the A. fulgidus Piwi protein

RNA interference (RNAi) is a conserved sequence-specific gene regulatory mechanism mediated by the RNA-induced silencing complex (RISC), which is composed of a single-stranded guide RNA and an Argonaute protein. The PIWI domain, a highly conserved motif within Argonaute, has been shown to adopt an RNase H fold critical for the endonuclease cleavage activity of RISC. Here we report the crystal structure of Archaeoglobus fulgidus Piwi protein bound to double-stranded RNA, thereby identifying the binding pocket for guide-strand 5'-end recognition and providing insight into guide-strand-mediated messenger RNA target recognition. The phosphorylated 5' end of the guide RNA is anchored within a highly conserved basic pocket, supplemented by the carboxy-terminal carboxylate and a bound divalent cation. The first nucleotide from the 5' end of the guide RNA is unpaired and stacks over a conserved tyrosine residue, whereas successive nucleotides form a four-base-pair RNA duplex. Mutation of the corresponding amino acids that contact the 5' phosphate in human Ago2 resulted in attenuated mRNA cleavage activity. Our structure of the Piwi-RNA complex, and that determined elsewhere, provide direct support for the 5' region of the guide RNA serving as a nucleation site for pairing with target mRNA and for a fixed distance separating the RISC-mediated mRNA cleavage site from the anchored 5' end of the guide RNA.     

一类非游荡算子的小扰动下的不变性

对于一种新型的线性混沌算子——非游荡算子,研究Banach空间上的一类特殊非游荡算子——可逆线性有界非游荡算子,证明它的小扰动下的不变性．利用矩阵和不变集的方法证明在非游荡算子的一充分小的领域内,非游荡算子保持它的非游荡性不变．即充分靠近非游荡线性算子的可逆线性算子是非游荡的．     

Major determinants of the specificity of interaction between small nuclear ribonucleoproteins U1A and U2B' and their cognate RNAs

The basis of the specificity of interaction of U1 and U2 small nuclear (sn)RNAs and their cognate binding proteins, U1A and U2B', has been examined. The U1A protein recognizes U1 snRNA on its own, whereas U2B' binds specifically to U2 snRNA only in the presence of a second protein, U2A'. Exchange of two nucleotides between the two RNAs or of eight amino acids between the two proteins reverses binding specificity.     

Chloride/proton antiporter activity of mammalian CLC proteins ClC-4 and ClC-5

ClC-4 and ClC-5 are members of the CLC gene family, with ClC-5 mutated in Dent's disease, a nephropathy associated with low-molecular-mass proteinuria and eventual renal failure. ClC-5 has been proposed to be an electrically shunting Cl- channel in early endosomes, facilitating intraluminal acidification. Motivated by the discovery that certain bacterial CLC proteins are secondary active Cl-/H+ antiporters, we hypothesized that mammalian CLC proteins might not be classical Cl- ion channels but might exhibit Cl(-)-coupled proton transport activity. Here we report that ClC-4 and ClC-5 carry a substantial amount of protons across the plasma membrane when activated by positive voltages, as revealed by measurements of pH close to the cell surface. Both proteins are able to extrude protons against their electrochemical gradient, demonstrating secondary active transport. H+, but not Cl-, transport was abolished when a pore glutamate was mutated to alanine (E211A). ClC-0, ClC-2 and ClC-Ka proteins showed no significant proton transport. The muscle channel ClC-1 exhibited a small H+ transport that might be physiologically relevant. For ClC-5, we estimated that Cl- and H+ transport contribute about equally to the total charge movement, raising the possibility that the coupled Cl-/H+ transport of ClC-4 and ClC-5 is of significant magnitude in vivo.     

A question of class

Fundamental misunderstandings about classification can lead scientists down unproductive or dangerous paths, argue Jeffrey Parsons and Yair Wand.     

核仁小分子RNA基因的起源初探

通过分析、比较含ＢｏｘＣ／Ｄ和含ＢｏｘＨ／ＡＣＡ这两类ｓｎｏＲＮＡ的一些代表与几种剪接体ｓｎＲＮＡ的序列和二级结构特征，研究它们的进化关系，并探讨ｓｎｏＲＮＡ是起源于内含子还是后来才插入到内含子中这一与ｓｎｏＲＮＡ的起源密切相关的问题．结合对剪接体ｓｎＲＮＡ起源的有关研究，提出两类ｓｎｏＲＮＡ最初是起源于原始Ⅱ类内含子中的不同部分的观点．     

Structure of human guanylate-binding protein 1 representing a unique class of GTP-binding proteins

Interferon-gamma is an immunomodulatory substance that induces the expression of many genes to orchestrate a cellular response and establish the antiviral state of the cell. Among the most abundant antiviral proteins induced by interferon-gamma are guanylate-binding proteins such as GBP1 and GBP2. These are large GTP-binding proteins of relative molecular mass 67,000 with a high-turnover GTPase activity and an antiviral effect. Here we have determined the crystal structure of full-length human GBP1 to 1.8 A resolution. The amino-terminal 278 residues constitute a modified G domain with a number of insertions compared to the canonical Ras structure, and the carboxy-terminal part is an extended helical domain with unique features. From the structure and biochemical experiments reported here, GBP1 appears to belong to the group of large GTP-binding proteins that includes Mx and dynamin, the common property of which is the ability to undergo oligomerization with a high concentration-dependent GTPase activity.