Assembly of Agrostemma githago (corn-cockle) storage proteins and their precursor proteins into oligomers.

Tyrosine-glycogen obtained from retina proteoglycogen by exhaustive proteolytic digestion was radiolabelled with 125I. The 125I-labelled tyrosine-glycogen was degraded by amylolytic digestion to a very small radioactive product, which was identified as iodotyrosine by h.p.l.c. The amylolytic mixture used released glucose and maltose that were alpha-linked to the phenolic hydroxy group of p-nitrophenol. No free iodotyrosine was found before or after the intact [125I]iodotyrosine-glycogen was subjected to two cycles of the Edman degradation procedure. The linkage between protein and glycogen was alkali-stable. Therefore it is concluded that the protein-bound glycogen was O-glycosidically linked to the phenolic hydroxy group of tyrosine. The amino acid has not been heretofore found to be involved in the linkage of carbohydrates to proteins.     

Structure and noncanonical activities of coat proteins of helical plant viruses

The main function of virus coat protein is formation of the capsid that protects the virus genome against degradation. However, besides the structural function, coat proteins have many additional important activities in the infection cycle of the virus and in the defense response of host plants to viral infection. This review focuses on noncanonical functions of coat proteins of helical RNA-containing plant viruses with positive genome polarity. Analysis of data on the structural organization of coat proteins of helical viruses has demonstrated that the presence of intrinsically disordered regions within the protein structure plays an important role in implementation of nonstructural functions and largely determines the multifunctionality of coat proteins.     

A dendrogram of plant viruses.

To facilitate the recognition of plant viruses with similar characteristics a dendrogram of characterized viruses was constructed. The sequence of criteria included: type of nucleic acid; single or double stranded; presence or absence of lipid envelope; helical or nonhelical symmetry; and divided or single genome. Nonhelical RNA viruses with divided genomes were further divided into viruses with one or more than one capsid size. Those with one capsid size were subdivided into viruses with one or more than one sedimenting component. Nonhelical RNA viruses with a single genome were divided according to their RNA size, and their sensitivity to sodium dodecyl sulfate and ethylenediaminetetraacetic acid.     

Sindbis virus proteins nsP1 and nsP2 contain homology to nonstructural proteins from several RNA plant viruses.

Although the genetic organization of tobacco mosaic virus (TMV) differs considerably from that of the tripartite viruses (alfalfa mosaic virus [AlMV] and brome mosaic virus [BMV]), all of these RNA plant viruses share three domains of homology among their nonstructural proteins. One such domain, common to the AlMV and BMV 2a proteins and the readthrough portion of TMV p183, is also homologous to the readthrough protein nsP4 of Sindbis virus (Haseloff et al., Proc. Natl. Acad. Sci. U.S.A. 81:4358-4362, 1984). Two more domains are conserved among the AlMV and BMV 1a proteins and TMV p126. We show here that these domains have homology with portions of the Sindbis proteins nsP1 and nsP2, respectively. These results strengthen the view that the four viruses share mechanistic similarities in their replication strategies and may be evolutionarily related. These results also suggest that either the AlMV 1a, BMV 1a, and TMV p126 proteins are multifunctional or Sindbis proteins nsP1 and nsP2 function together as subunits in a single complex.     

Plasmodesmata and plant viruses. A centenary story.

The passage of plant viruses from a cell to adjacent ones remained for a long time an unexplained event. Only during the thirties did Samuel and other plant virologists put forward the hypothesis that the passage occurred through plasmodesmata, i.e. those protoplasmic connections between plant cells described since the late 19th century. A direct relation between viruses and plasmodesmata was first demonstrated by electron microscopy during the late 1960s by Esau and co-workers, and then widely confirmed. The mechanism of the passage was investigated in depth starting from the 1970s, and research received a remarkable impulse after that a well-defined model of plasmodesmata had been obtained thank, in particular, to work of the Robards' and Gunning's groups. In this context, the discovery of the polycystronic functionality of the viral genomes was fundamental. A protein coded by tobacco mosaic virus, discovered in 1982 independently by the Soviet group of Atabekov and the American group of Zaitlin, was demonstrated to be indispensable for the transport of virus infection from cell to cell through plasmodesmata. Elegant investigations on this 'movement protein' demonstrated that it actually increases the permeability of plasmodesmata. The relation between viruses and plasmodesmata is one of the most interesting and investigated theme of research, which is receiving much attention from plant virologists, physiologists and molecular biologists. The current status of knowledge still presents unsolved questions, and the story is far from over.     

RNA recombination in animal and plant viruses.

An increasing number of animal and plant viruses have been shown to undergo RNA-RNA recombination, which is defined as the exchange of genetic information between nonsegmented RNAs. Only some of these viruses have been shown to undergo recombination in experimental infection of tissue culture, animals, and plants. However, a survey of viral RNA structure and sequences suggests that many RNA viruses were derived form homologous or nonhomologous recombination between viruses or between viruses and cellular genes during natural viral evolution. The high frequency and widespread nature of RNA recombination indicate that this phenomenon plays a more significant role in the biology of RNA viruses than was previously recognized. Three types of RNA recombination are defined: homologous recombination; aberrant homologous recombination, which results in sequence duplication, insertion, or deletion during recombination; and nonhomologous (illegitimate) recombination, which does not involve sequence homology. RNA recombination has been shown to occur by a copy choice mechanism in some viruses. A model for this recombination mechanism is presented.     

Assembly of a spherical plant virus.

The conditions previously reported as necessary for the reassembly of spherical viruses have been distinctly unphysiological and such reassembly cannot be related directly to the in vivo reaction. Mild conditions for the in vitro reassembly of cowpea chlorotic mottle virus (CCMV) from its isolated components have now been described (Adolph & Butler 1975) and the reassembled virus characterized. This reassembly involved the co-aggregation of the RNA and protein around neutrality and at ionic strength 0.2, giving yields of 70% encapsidation at pH 6.0. The reaction was independent of temperature over the range 5-25 degrees C and did not require the presence of Mg2+ ions. The reassembled virus shows a stability similar to that of native CCMV, with the same change in sedimentation coefficient around pH 6.5. The molecular mass and buoyant density in CsCl are also the same as those of native CCMV, while the electron microscope reveals a surface morphology on the reassembled particles like that on native CCMV. Analysis of the number-average, mass-average, and Z-average molecular masses of the purified protein at both pH 6.0 and pH 7.5 suggests that the active unit for reassembly is a dimer of the protein subunit.     

Coat proteins of two filamentous plant viruses display NTPase activity in vitro

Coat proteins (CPs) of plant viruses are involved in different stages of the viral life cycle such as virion assembly, replication, movement, vector transmission, and regulation of host defense responses. Here, we report that the CPs of two filamentous RNA viruses, potato virus X (PVX, Potexvirus) and potato virus A (PVA, Potyvirus) exhibit an enzyme activity. The CP isolated from PVX virions possesses ATP-binding and ATPase activities. Recombinant PVX and PVA CPs produced in Escherichia coli show Mg2+-dependent ATPase and UTPase activities inhibited by antibodies against virus particles. Deletion of the C-terminal regions of these proteins diminishes their ATPase activity.     

抗冻蛋白及其在植物抗冻基因工程的应用

从应用的角度系统综述了抗冻蛋白（ＡＦＰs)的特性、活性、用途、生化特征、在细菌中的表达,在植物抗冻生理中的作用及其基因工程,简洁地讨论了抗冻蛋白的研究现状和最新进展。     

Lifestyles of plant viruses

The vast majority of well-characterized eukaryotic viruses are those that cause acute or chronic infections in humans and domestic plants and animals. However, asymptomatic persistent viruses have been described in animals, and are thought to be sources for emerging acute viruses. Although not previously described in these terms, there are also many viruses of plants that maintain a persistent lifestyle. They have been largely ignored because they do not generally cause disease. The persistent viruses in plants belong to the family Partitiviridae or the genus Endornavirus. These groups also have members that infect fungi. Phylogenetic analysis of the partitivirus RNA-dependent RNA polymerase genes suggests that these viruses have been transmitted between plants and fungi. Additional families of viruses traditionally thought to be fungal viruses are also found frequently in plants, and may represent a similar scenario of persistent lifestyles, and some acute or chronic viruses of crop plants may maintain a persistent lifestyle in wild plants. Persistent, chronic and acute lifestyles of plant viruses are contrasted from both a functional and evolutionary perspective, and the potential role of these lifestyles in host evolution is discussed.     

Mechanisms of arthropod transmission of plant and animal viruses.

A majority of the plant-infecting viruses and many of the animal-infecting viruses are dependent upon arthropod vectors for transmission between hosts and/or as alternative hosts. The viruses have evolved specific associations with their vectors, and we are beginning to understand the underlying mechanisms that regulate the virus transmission process. A majority of plant viruses are carried on the cuticle lining of a vector's mouthparts or foregut. This initially appeared to be simple mechanical contamination, but it is now known to be a biologically complex interaction between specific virus proteins and as yet unidentified vector cuticle-associated compounds. Numerous other plant viruses and the majority of animal viruses are carried within the body of the vector. These viruses have evolved specific mechanisms to enable them to be transported through multiple tissues and to evade vector defenses. In response, vector species have evolved so that not all individuals within a species are susceptible to virus infection or can serve as a competent vector. Not only are the virus components of the transmission process being identified, but also the genetic and physiological components of the vectors which determine their ability to be used successfully by the virus are being elucidated. The mechanisms of arthropod-virus associations are many and complex, but common themes are beginning to emerge which may allow the development of novel strategies to ultimately control epidemics caused by arthropod-borne viruses.