The expression of the TMV-specific 30-kDa protein in tobacco protoplasts is strongly and selectively enhanced by actinomycin

An Alliance of Gel-Based and Gel-Free Proteomic Techniques Displays Substantial Insight Into the Proteome of a Virulent and an Attenuated Histomonas meleagridis Strain

The unicellular protozoan Histomonas meleagridis is notorious for being the causative agent of histomonosis, which can cause high mortality in turkeys and substantial production losses in chickens. The complete absence of commercially available curative strategies against the disease renders the devising of novel approaches a necessity. A fundamental step toward this objective is to understand the flagellate's virulence and attenuation mechanisms. For this purpose we have previously conducted a comparative proteomic analysis of an in vitro cultivated virulent and attenuated histomonad parasite using two-dimensional electrophoresis and MALDI-TOF/TOF. The current work aimed to substantially extend the knowledge of the flagellate's proteome by applying 2D-DIGE and sequential window acquisition of all theoretical mass spectra (SWATH) MS as tools on the two well-defined strains. In the gel-based experiments, 49 identified protein spots were found to be differentially expressed, of which 37 belonged to the in vitro cultivated virulent strain and 12 to the attenuated one. The most frequently identified proteins in the virulent strain take part in cytoskeleton formation, carbohydrate metabolism and adaptation to stress. However, post-translationally modified or truncated ubiquitous cellular proteins such as actin and GAPDH were identified as upregulated in multiple gel positions. This indicated their contribution to processes not related to cytoskeleton and carbohydrate metabolism, such as fibronectin or plasminogen binding. Proteins involved in cell division and cytoskeleton organization were frequently observed in the attenuated strain. The findings of the gel-based studies were supplemented by the gel-free SWATH MS analysis, which identified and quantified 42 significantly differentially regulated proteins. In this case proteins with peptidase activity, metabolic proteins and actin-regulating proteins were the most frequent findings in the virulent strain, while proteins involved in hydrogenosomal carbohydrate metabolism dominated the results in the attenuated one.

Potential Pathways Involved in Elaidic Acid Induced Atherosclerosis in Human Umbilical Vein Endothelial Cells

Researches have demonstrated that trans-fatty acids are related to the progression of atherosclerosis, but the underlying mechanism is not clear till now. In the presented study, two-dimensional electrophoresis based proteomics was used to discover the role of elaidic acid in atherosclerosis. In human umbilical vein endothelial cells (HUVEC), twenty-two and twenty-three differentially expressed proteins were identified in low (50 μmol/L) and high (400 μmol/L) concentration elaidic acid simulated groups, respectively, comparing with the control group. The expressions of some selected proteins (PSME3, XRCC5, GSTP1, and GSTO1) were validated by qRT-PCR analysis. Western blotting analysis further confirmed that elaidic acid downregulated the expression of PSME3and XRCC5. Moreover, P53, the downstream protein of PSME3, was further investigated. Results demonstrated that a variety of proteins, many of which were related to oxidative stress, apoptosis, and DNA damage, were involved in the elaidic acid induced atherosclerosis. Furthermore, P53 was demonstrated to regulate the atherosclerosis through cell cycle arrest and apoptosis pathway.

Bordetella pertussis Isolates from Argentinean Whooping Cough Patients Display Enhanced Biofilm Formation Capacity Compared to Tohama I Reference Strain

Pertussis is a highly contagious disease mainly caused by Bordetella pertussis. Despite the massive use of vaccines, since the 1950s the disease has become re-emergent in 2000 with a shift in incidence from infants to adolescents and adults. Clearly, the efficacy of current cellular or acellular vaccines, formulated from bacteria grown in stirred bioreactors is limited, presenting a challenge for future vaccine development. For gaining insights into the role of B. pertussis biofilm development for host colonization and persistence within the host, we examined the biofilm forming capacity of eight argentinean clinical isolates recovered from 2001 to 2007. All clinical isolates showed an enhanced potential for biofilm formation compared to the reference strain Tohama I. We further selected the clinical isolate B. pertussis 2723, exhibiting the highest biofilm biomass production, for quantitative proteomic profiling by means of two-dimensional fluorescence difference gel electrophoresis (2D-DIGE) coupled with mass spectrometry, which was accompanied by targeted transcriptional analysis. Results revealed an elevated expression of several virulence factors, including adhesins involved in biofilm development. In addition, we observed a higher expression of energy metabolism enzymes in the clinical isolate compared to the Tohama I strain. Furthermore, all clinical isolates carried a polymorphism in the bvgS gene. This mutation was associated to an increased sensitivity to modulation and a faster rate of adhesion to abiotic surfaces. Thus, the phenotypic biofilm characteristics shown by the clinical isolates might represent an important, hitherto underestimated, adaptive strategy for host colonization and long time persistence within the host.

Proteome of tolerance fine-tuning in the human pathogen black yeast Exophiala dermatitidis

The black yeast Exophiala dermatitidis is a worldwide distributed agent of primary and secondary diseases in both immunocompromised and healthy humans, with a high prevalence in human-made environments. Since thermo-tolerance has a crucial role in the fungus persistence in man-dominated habitat and in its pathogenicity, three incubation temperatures (37, 45, 1 °C) and two time spans (1 h, 1 week) were selected to simulate different environmental conditions and to investigate the effect of temperature on the proteome of E. dermatitidis CBS 525.76. Using a novel protocol for protein extraction from black yeasts, 2-D DIGE could be applied for characterization of changes in total protein spot abundance among the experimental conditions. A total of 32 variable proteins were identified by mass spectrometry. Data about protein functions, localization and pathways were also obtained. A typical stress response under non-optimal temperature could not be observed at the proteome level, whereas a reduction of the metabolic activity, mostly concerning processes as the general carbon metabolism, was detected after exposure to cold. These results suggest that a fine protein modulation takes place following temperature treatment and a repertoire of stable protein might be at the base of E. dermatitidis adaptation to altered growth conditions.

SIGNIFICANCE

E. dermatitidis is a pathogenic black yeast causing neurotropic infections, systemic and subcutaneous disease in a wide range of hosts, including humans. The discovery of the fungus high prevalence in man-made habitats, including sauna facilities, drinking water and dishwashers, generated concern and raised questions about the infection route. In the present work - which is the first contribution on E. dermatitidis proteome - the effect of different temperature conditions on the fungus protein pattern have been analyzed by using a gel-based approach and the temperature responsive proteins have been identified. The absence of a typical stress response following the exposure to non-optimal temperature was detected at the proteome level, along with a general reduction of the metabolic activity after exposure to cold. These results suggest that a very fine regulation of the protein expression as well as adaptations involving a basic set of stable proteins may be at the base of E. dermatitidis enormous ecological plasticity, which plays a role in the fungus distribution, also enabling the transition from natural to human habitat and to the human host.

A comparative proteome analysis links tyrosine kinase 2 (Tyk2) to the regulation of cellular glucose and lipid metabolism in response to poly(I:C)

Tyrosine kinase 2 (Tyk2) is an integral part of the Janus kinase-signal transducer and activator of transcription (JAK-STAT) pathway which relays intracellular signals of various cytokines. Tyk2 crucially contributes to host defense mechanisms against microbial pathogens and to tumor surveillance but also facilitates immune pathologies. Here we investigated the impact of Tyk2 on the macrophage proteome using the synthetic double-stranded RNA analog polyinosinic acid-polycytidylic acid (poly(I:C)) as a mimicry of viral infections. By means of 2D-DIGE in connection with PMF obtained by MALDI-MS and sequence tag determination by MS/MS we unambiguously identified eighteen protein spots corresponding to sixteen distinct proteins that are regulated by poly(I:C) and differentially expressed between wildtype (WT) and Tyk2-deficient macrophages. The majority of these proteins are functionally assigned to cellular immune responses and to metabolism. We show for selected metabolic enzymes, i.e. triosephosphate isomerase (TIM), ATP-citrate synthase (ACLY) and long-chain-fatty-acid-CoA ligase 4 (ACSL4), that Tyk2 affects protein expression transcriptionally and post-transcriptionally. We furthermore confirm the involvement of Tyk2 in the regulation of lipid and carbohydrate metabolism at the level of metabolites. Taken together, our results provide new evidence for important functions of Tyk2 at the molecular interface between innate immunity and cellular metabolism.

Cellular pathways for viral transport through plasmodesmata

Plant viruses use plasmodesmata (PD) to spread infection between cells and systemically. Dependent on viral species, movement through PD can occur in virion or non-virion form, and requires different mechanisms for targeting and modification of the pore. These mechanisms are supported by viral movement proteins and by other virus-encoded factors that interact among themselves and with plant cellular components to facilitate virus movement in a coordinated and regulated fashion.

NTH201, a novel class II KNOTTED1-like protein, facilitates the cell-to-cell movement of Tobacco mosaic virus in tobacco

NTH201, a novel class II KNOTTED1-like protein gene, was cloned from tobacco (Nicotiana tabacum cv. Xanthi) and its role in Tobacco mosaic virus (TMV) infection was analyzed. Virus-induced gene silencing of NTH201 caused a delay in viral RNA accumulation as well as virus spread in infected tobacco plants. Overexpression of the gene in a transgenic tobacco plant (N. tabacum cv. Xanthi nc) infected by TMV showed larger local lesions than those of the nontransgenic plant. NTH201 exhibited no intercellular trafficking ability but did exhibit colocalization with movement protein (MP) at the plasmodesmata. When NTH201-overexpressing tobacco BY-2 cultured cells were infected with TMV, the accumulation of MP but not of viral genomic and subgenomic RNA clearly was accelerated compared with those in nontransgenic cells at an early infection period. The formation of virus replication complexes (VRC) also was accelerated in these transgenic cells. Conversely, NTH201-silenced cells showed less MP accumulations and fewer VRC formations than did nontransgenic cells. These results suggested that NTH201 might indirectly facilitate MP accumulation and VRC formation in TMV-infected cells, leading to rapid viral cell-to-cell movement in plants at an early infection stage.

Inhibition of bacterial transglutaminase by its heat-treated pro-enzyme

Transglutaminases form a unique family of cross-linking enzymes which may be interesting for pharmaceutical and technical purposes. Bacterial transglutaminase, differing from the eucaryotic counterparts in being independent from Ca2+ ions, is excreted by several Streptomyces species. Until now an endogenous factor regulating activated transglutaminase could not be detected. Here, we investigated whether an inhibitor of transglutaminase is excreted into the culture fluid of Streptomyces mobaraensis. We could demonstrate that heat-resistant inhibitory activity is produced after 24h of growth reaching a maximum after 72h. A two-step ion exchange chromatography purification procedure revealed co-elution of the heat-treated inhibitor with pro-transglutaminase. Experiments with wild-type and recombinant pro-transglutaminase confirmed that the precursor protein indeed inhibits the activity of the mature enzyme.

Proteomics in pancreatic disease

Proteomics represents a novel methodological approach to investigate the expression of all proteins by a cell or organism in its entireness, similar to global strategies for DNA (genomics) and RNA (transcriptomics). This review focuses on the history of protein analysis, which made up the golden age of pancreatic physiology, the current methodology for proteomics (2D gel electrophoresis, mass spectrometry) and the few published experiences with proteomics in the field of pancreatology until now. Finally, potential applications of proteomics for the pancreas, in concert with other techniques, are cited.

Oxygen tension regulates the expression of a group of procollagen hydroxylases

In this study, we have characterized the influence of hypoxia on the expression of hydroxylases crucially involved in collagen fiber formation, such as prolyl-4-hydroxylases (Ph4) and procollagen lysyl-hydroxylases (PLOD). Using the rat vascular smooth muscle cell line A7r5, we found that an hypoxic atmosphere caused a characteristic time-dependent five- to 12-fold up-regulation of the mRNAs of the two P4h alpha-subunits [alphaI (P4ha1) and alphaII (P4ha2)] and of two lysylhydroxylases (PLOD1 and PLOD2). These effects of hypoxia were mimicked by the iron-chelator deferoxamine (100 micro m) and by cobaltous chloride (100 micro m). The hypoxic induction of these genes was also seen in the mouse juxtaglomerular As4.1 cell line and mouse hepatoma cell line Hepa1 but was almost absent in the mutant cell line Hepa1C4, which is defective for the hypoxia-inducible transcription factor 1 (HIF-1). In addition, the enzyme expression was induced by hypoxia in mouse embryonic fibroblasts but not in embryonic fibroblasts lacking the HIF-1alpha subunit. These findings indicate that hypoxia stimulates the gene expression of a cluster of hydroxylases that are indispensible for collagen fiber formation. Strong indirect evidence, moreover, suggests that the expression of these enzymes during hypoxia is coordinated by HIF-1.

The yersinia virulence factor YopM forms a novel protein complex with two cellular kinases

Pathogenic Yersinia contain a virulence plasmid that encodes genes for intracellular effectors, which neutralize the host immune response. One effector, YopM, is necessary for Yersinia virulence, but its function in host cells is unknown. To identify potential cellular pathways affected by YopM, proteins that co-immunoprecipitate with YopM in mammalian cells were isolated and identified by mass spectrometry. Results demonstrate that two kinases, protein kinase C-like 2 (PRK2) and ribosomal S6 protein kinase 1 (RSK1), interact directly with YopM. These two kinases associate only when YopM is present, and expression of YopM in cells stimulates the activity of both kinases. RSK1 is activated directly by interaction with YopM, and RSK1 kinase activity is required for YopM-stimulated PRK2 activity. YopM activation of RSK1 occurs independently of the actions of YopJ on the MAPK pathway. YopM is also required for Yersinia-induced changes in RSK1 mobility in infected macrophage cells. These results identify the first intracellular targets of YopM and suggest YopM acts to stimulate the activity of PRK2 and RSK1.

The cellular oxygen tension regulates expression of the endoplasmic oxidoreductase ERO1-Lalpha

The formation of disulfide bonds in the endoplasmic reticulum requires protein disulfide isomerase (PDI) and endoplasmic reticulum oxidoreductin 1 (ERO1) that reoxidizes PDI. We report here that the expression of the rat, mouse and human homologues of ERO1-Like protein alpha but not of the isoform ERO1-Lbeta are stimulated by hypoxia in rats vivo and in rat, mouse and human cell cultures. The temporal pattern of hypoxic ERO1-Lalpha induction is very similar to that of genes triggered by the hypoxia inducible transcription factor (HIF-1) and is characteristically mimicked by cobalt and by deferoxamine, but is absent in cells with a defective aryl hydrocarbon receptor translocator (ARNT, HIF-1beta). We speculate from these findings that the expression of ERO1-Lalpha is probably regulated via the HIF-pathway and thus belongs to the family of classic oxygen regulated genes. Activation of the unfolded protein response (UPR) by tunicamycin, on the other hand, strongly induced ERO1-Lbeta and more moderately ERO1-Lalpha expression. The expression of the two ERO1-L isoforms therefore appears to be differently regulated, in the way that ERO1-Lalpha expression is mainly controlled by the cellular oxygen tension, whilst ERO1-Lbeta is triggered mainly by UPR. The physiological meaning of the oxygen regulation of ERO1-Lalpha expression likely is to maintain the transfer rate of oxidizing equivalents to PDI in situations of an altered cellular redox state induced by changes of the cellular oxygen tension.

Intramolecular complementing mutations in tobacco mosaic virus movement protein confirm a role for microtubule association in viral RNA transport

The movement protein (MP) of Tobacco mosaic virus (TMV) facilitates the cell-to-cell transport of the viral RNA genome through plasmodesmata (Pd). A previous report described the functional reversion of a dysfunctional mutation in MP (Pro81Ser) by two additional amino acid substitution mutations (Thr104Ile and Arg167Lys). To further explore the mechanism underlying this intramolecular complementation event, the mutations were introduced into a virus derivative expressing the MP as a fusion to green fluorescent protein (GFP). Microscopic analysis of infected protoplasts and of infection sites in leaves of MP-transgenic Nicotiana benthamiana indicates that MP(P81S)-GFP and MP(P81S;T104I;R167K)-GFP differ in subcellular distribution. MP(P81S)-GFP lacks specific sites of accumulation in protoplasts and, in epidermal cells, exclusively localizes to Pd. MP(P81S;T104I;R167K)-GFP, in contrast, in addition localizes to inclusion bodies and microtubules and thus exhibits a subcellular localization pattern that is similar, if not identical, to the pattern reported for wild-type MP-GFP. Since accumulation of MP to inclusion bodies is not required for function, these observations confirm a role for microtubules in TMV RNA cell-to-cell transport.

A dysfunctional movement protein of tobacco mosaic virus interferes with targeting of wild-type movement protein to microtubules

The Tobacco mosaic virus (TMV) movement protein (MPTMV) mediates cell-to-cell viral trafficking by altering properties of the plasmodesmata (Pd) in infected cells. During the infection cycle, MPTMV becomes transiently associated with endomembranes, microfilaments, and microtubules (MT). It has been shown that the cell-to-cell spread of TMV is reduced in plants expressing the dysfunctional MP mutant MPNT-1. To expand our understanding of the MP function, we analyzed events occurring during the intracellular and intercellular targeting of MPTMV and MPNT-1 when expressed as a fusion protein to green fluorescent protein (GFP), either by biolistic bombardment in a viral-free system or from a recombinant virus. The accumulation of MPTMV:GFP, when expressed in a viral-free system, is similar to MPTMV:GFP in TMV-infected tissues. Pd localization and cell-to-cell spread are late events, occurring only after accumulation of MP:GFP in aggregate bodies and on MT in the target cell. MPNT-1:GFP localizes to MT but does not target to Pd nor does it move cell to cell. The spread of transiently expressed MPTMV:GFP in leaves of transgenic plants that produce MPNT-1 is reduced, and targeting of the MPTMV:GFP to the cytoskeleton is inhibited. Although MPTMV:GFP targets to the Pd in these plants, it is partially impaired for movement. It has been suggested that MPNT-1 interferes with host-dependent processes that occur during the intracellular targeting program that makes MP movement competent.

Cellular targets of functional and dysfunctional mutants of tobacco mosaic virus movement protein fused to green fluorescent protein

Intercellular transport of tobacco mosaic virus (TMV) RNA involves the accumulation of virus-encoded movement protein (MP) in plasmodesmata (Pd), in endoplasmic reticulum (ER)-derived inclusion bodies, and on microtubules. The functional significance of these interactions in viral RNA (vRNA) movement was tested in planta and in protoplasts with TMV derivatives expressing N- and C-terminal deletion mutants of MP fused to the green fluorescent protein. Deletion of 55 amino acids from the C terminus of MP did not interfere with the vRNA transport function of MP:GFP but abolished its accumulation in inclusion bodies, indicating that accumulation of MP at these ER-derived sites is not a requirement for function in vRNA intercellular movement. Deletion of 66 amino acids from the C terminus of MP inactivated the protein, and viral infection occurred only upon complementation in plants transgenic for MP. The functional deficiency of the mutant protein correlated with its inability to associate with microtubules and, independently, with its absence from Pd at the leading edge of infection. Inactivation of MP by N-terminal deletions was correlated with the inability of the protein to target Pd throughout the infection site, whereas its associations with microtubules and inclusion bodies were unaffected. The observations support a role of MP-interacting microtubules in TMV RNA movement and indicate that MP targets microtubules and Pd by independent mechanisms. Moreover, accumulation of MP in Pd late in infection is insufficient to support viral movement, confirming that intercellular transport of vRNA relies on the presence of MP in Pd at the leading edge of infection.

Replication of tobacco mosaic virus RNA

The replication of tobacco mosaic virus (TMV) RNA involves synthesis of a negative-strand RNA using the genomic positive-strand RNA as a template, followed by the synthesis of positive-strand RNA on the negative-strand RNA templates. Intermediates of replication isolated from infected cells include completely double-stranded RNA (replicative form) and partly double-stranded and partly single-stranded RNA (replicative intermediate), but it is not known whether these structures are double-stranded or largely single-stranded in vivo. The synthesis of negative strands ceases before that of positive strands, and positive and negative strands may be synthesized by two different polymerases. The genomic-length negative strand also serves as a template for the synthesis of subgenomic mRNAs for the virus movement and coat proteins. Both the virus-encoded 126-kDa protein, which has amino-acid sequence motifs typical of methyltransferases and helicases, and the 183-kDa protein, which has additional motifs characteristic of RNA-dependent RNA polymerases, are required for efficient TMV RNA replication. Purified TMV RNA polymerase also contains a host protein serologically related to the RNA-binding subunit of the yeast translational initiation factor, eIF3. Study of Arabidopsis mutants defective in RNA replication indicates that at least two host proteins are needed for TMV RNA replication. The tomato resistance gene Tm-1 may also encode a mutant form of a host protein component of the TMV replicase. TMV replicase complexes are located on the endoplasmic reticulum in close association with the cytoskeleton in cytoplasmic bodies called viroplasms, which mature to produce 'X bodies'. Viroplasms are sites of both RNA replication and protein synthesis, and may provide compartments in which the various stages of the virus mutiplication cycle (protein synthesis, RNA replication, virus movement, encapsidation) are localized and coordinated. Membranes may also be important for the configuration of the replicase with respect to initiation of RNA synthesis, and synthesis and release of progeny single-stranded RNA.

Distribution of TMV movement protein in single living protoplasts immobilized in agarose

Recent studies of the tobacco mosaic virus (TMV) P30 movement protein (MP) fused with green fluorescent protein (GFP) during TMV infection described the involvement of elements of the cytoskeleton and components of the endoplasmic reticulum (ER) in the intracellular trafficking of MP:GFP from the sites of synthesis in the cytoplasm to plasmodesmata. To examine in real-time the pattern of synthesis, accumulation and degradation of MP:GFP, we developed a method to immobilize protoplasts in agarose such that they are maintained alive for extended periods of time. The pattern of MP:GFP accumulation in single living protoplasts visualized by confocal laser scanning microscopy (CLSM) was parallel to that previously described in a population of protoplasts harvested at different times post-infection. Additionally, a network of weakly fluorescent filaments, which are apparently different from microtubules, was observed to surround the nucleus and these filaments were associated with fluorescent bodies (previously identified as ER-derived structures). Later in infection, the fluorescent bodies increased in size and coalesced to form larger structures that accumulated near the periphery of the cells while highly fluorescent non-cortical filaments were observed distributed in the cytoplasm. The putative involvement of these filaments in targeting the fluorescent bodies to the periphery of the cell is discussed. Studies of single, embedded protoplasts make it possible to observe changes in amount and subcellular localization of viral and other proteins.

Nontranslatability and dissimilar behavior in plants and protoplasts of viral RNA and movement protein complexes formed in vitro

It was found that the fusion (His)6-movement proteins (MPs) of two tobamoviruses (TMV UI and a crucifer-infecting tobamovirus, crTMV) were efficient nonspecific translational repressors. The in vitro translation of viral RNAs was blocked by incomplete 30K MP-RNA complexes formed at the MP:RNA molar ratios of 100-150:1. Similar results were obtained with the barley stripe mosaic hordeivirus (BSMV)-encoded 58K MP; however, the translation inhibiting activity of the 58K MP was manifested only in the presence of magnesium. By contrast, the 25K MP of potato virus X (PVX) was incapable of forming MP-RNA complexes under experimental conditions used and did not inhibit in vitro translation. The translation repressing ability correlated with the level of MP affinity to RNA. The complexes of the 30K MP and 58K MP with TMV RNA were not infectious in isolated protoplasts; however, they were infectious in indicator plants. Reduction of MP affinity to RNA resulted in translatability of MP-TMV RNA complexes that apparently was due to their destabilization. Thus, the deletion mutant DEL4 MP formed MP-TMV RNA complexes that were translatable in vitro, infectious to protoplasts and plants. In contrast to this, the complexes of TMV RNA with the mammalian RNA-binding protein p50 were nontranslatable and noninfectious to either protoplasts or intact plants. These results implied that nontranslatable MP-RNA complexes which could not replicate in the primary infected cells were converted into a translatable and replicatable form in the course of passage through plasmodesmata in planta.

The 126- and 183-kilodalton proteins of tobacco mosaic virus, and not their common nucleotide sequence, control mosaic symptom formation in tobacco

Nucleotide substitutions at two positions within the open reading frame encoding the 126-kDa protein in the attenuated masked (M) strain of tobacco mosaic tobamovirus (TMV) to those found in the virulent U1-TMV genome led to the induction of near U1-TMV-like symptoms on leaves of Nicotiana tabacum L. cv. Xanthi nn by progeny virus (M. H. Shintaku, S. A. Carter, Y. Bao, and R. S. Nelson, Virology 221:218-225, 1996). In this study, further site-directed mutations were made at these positions within the M strain cDNA to determine whether the protein or nucleotide sequence directly controlled the symptom phenotype. The protein and not the nucleotide sequence directly controlled the symptom phenotype when amino acid 360 within the 126-kDa protein sequence was altered and likely controlled the symptom phenotype when amino acid 601 was altered. The effects of the substitutions at amino acid position 360 on viral protein accumulation were studied by pulse-labeling proteins in infected protoplasts. Accumulation of the 126- and 183-kDa proteins was less for an attenuated mutant than for two virulent mutants, but the viral movement protein and coat protein accumulated to levels reported to be sufficient for normal systemic symptom development. The size of necrotic local lesions on N. tabacum L. cv. Xanthi NN was negatively correlated with symptom development and accumulation of the 126-kDa protein for these mutants. With reference to this last finding, an explanation of the cause of the differing symptoms induced by these viruses is presented.

Comparison of the replication of positive-stranded RNA viruses of plants and animals

It is clear from the experimental data that there are some similarities in RNA replication for all eukaryotic positive-stranded RNA viruses—that is, the mechanism of polymerization of the nucleotides is probably similar for all. It is noteworthy that all mechanisms appear to utilize host membranes as a site of replication. Membranes appear to function not only as a way of compartmentalizing virus RNA replication but also appear to have a central role in the organization and functioning of the replication complex, and further studies in this area are needed. Within virus supergroups, similarities are evident between animal and plant viruses—for example, in the nature and arrangements of replication genes and in sequence similarities of functional domains. However, it is also clear that there has been considerable divergence, even within supergroups. For example, the animal alpha-viruses have evolved to encode proteinases which play a central controlling function in the replication cycle, whereas this is not common in the plant alpha-like viruses and even when it occurs, as in the tymoviruses, the strategies that have evolved appear to be significantly different. Some of the divergence could be host-dependent and the increasing interest in the role of host proteins in replication should be fruitful in revealing how different systems have evolved. Finally, there are virus supergroups that appear to have no close relatives between animals and plants, such as the animal coronavirus-like supergroup and the plant carmo-like supergroup.

Regulation of tobamovirus gene expression

This chapter discusses tobacco mosaic virus (TMV) strains U1, OM, L, CGMMV, 0, and Cc. The production of each TMV protein is regulated differently, both in amounts and times of production. The chapter discusses some of the strategies that tobamoviruses uses to control gene expression: (1) different subgenomic RNA promoter/leader sequences control timing of expression of genes, (2) genes expressed via subgenomic mRNAs are expressed in decreasing amounts with increasing distances from the 3' terminus, and (3) TMV mRNAs appear to be translationally regulated differently from host mRNAs. Genome organization affects gene expression, but it appears to be equally important for the efficiency of replication and the ability of the genomic structure to be stably propagated. Different virus groups have evolved different gene arrangements. Tobamovirus genes expressed via subgenomic mRNAs appear to be expressed in increasing amounts when positioned nearer the 3’ terminus.

Time course of TMV 30K protein accumulation in intact leaves

The kinetics of accumulation of the 30K and coat proteins of tobacco mosaic virus (TMV) which are expressed via subgenomic mRNAs were determined in near-synchronously infected cells of intact tobacco leaves. The 30K protein accumulated to maximal levels during the early stages of the infection as previously reported in tobacco protoplasts. However, in intact leaves, 30K protein accumulated for longer periods and attained higher concentrations than in protoplasts, remaining detectable in all later time samples. Detection of the coat protein, and also the 126K and 183K proteins, began at approximately the same time as the 30K protein (9-12 hr after initiation of replication), but their accumulation continued throughout the 72-hr sampling period. Most of the 30K protein accumulated before 24 hr, whereas most of the coat protein accumulated after 24 hr. This confirms that these two genes are regulated differently, both temporally and quantitatively.