Nucleotide sequence of the coat protein cistron and the 3' noncoding region of cucumber green mottle mosaic virus (watermelon strain) RNA

Transcriptome analysis of watermelon (Citrullus lanatus) fruits in response to Cucumber green mottle mosaic virus (CGMMV) infection

Cucumber green mottle mosaic virus (CGMMV) belongs to the Tobamovirus genus and is a major global plant virus on cucurbit plants. It causes severe disease symptoms on infected watermelon plants (Citrullus lanatus), particularly inducing fruit decay. However, little is known about the molecular mechanism of CGMMV-induced watermelon fruit decay. For this study, comparative analysis of transcriptome profiles of CGMMV-inoculated and mock-inoculated watermelon fruits were conducted via RNA-Seq. A total of 1,621 differently expressed genes (DEGs) were identified in CGMMV-inoculated watermelon, among which 1,052 were up-regulated and 569 were down-regulated. Functional annotation analysis showed that several DEGs were involved in carbohydrate metabolism, hormone biosynthesis and signaling transduction, secondary metabolites biosynthesis, and plant-pathogen interactions. We furthermore found that some DEGs were related to cell wall components and photosynthesis, which may directly be involve in the development of the symptoms associated with diseased watermelons. To confirm the RNA-Seq data, 15 DEGs were selected for gene expression analysis by qRT-PCR. The results showed a strong correlation between these two sets of data. Our study identified many candidate genes for further functional studies during CGMMV-watermelon interactions, and will furthermore help to clarify the understanding of pathogenic mechanism underlying CGMMV infection in cucurbit plants.

Studies on the Conformation of a Polyelectrolyte in Solution: Local Conformation of Cucumber Green Mottle Mosaic Virus RNA Compared with Tobacco Mosaic Virus RNA

The thermal stability of the local structures of cucumber green mottle mosaic virus RNA, CGMMV-RNA, and tobacco mosaic virus RNA, TMV-RNA, was studied by circular dichroism (CD) and small-angle X-ray scattering (SAXS) and compared with each other in the temperature domain from 20 to 50 degrees C. The temperature dependence of the molar ellipticity and mean-square radius of the cross section of a chain shows that the structure of CGMMV-RNA is more vulnerable than that of TMV-RNA. Such a different thermal stability of their structures was also reflected in the temperature dependence of the length and number of the constituent rods when the structures of the two RNA chains were represented by a model which consisted of rods joined with freely hinged joints. From these results, a possibility was suggested that the structural stability of CGMMV-RNA and TMV-RNA might be correlated with the infectivity of the corresponding virus, CGMMV and TMV, respectively.

Proton dependence of tobacco mosaic virus dissociation by pressure

Tobacco mosaic virus (TMV) is an intensely studied model of viruses. This paper reports an investigation into the dissociation of TMV by pH and pressure up to 220 MPa. The viral solution (0.25 mg/ml) incubated at 277 K showed a significant decrease in light scattering with increasing pH, suggesting dissociation. This observation was confirmed by HPLC gel filtration and electron microscopy. The calculated volume change of dissociation (DeltaV) decreased (absolute value) from -49.7 ml/mol of subunit at pH 3.8 to -21.7 ml/mol of subunit at pH 9.0. The decrease from pH 9.0 to 3.8 caused a stabilization of 14.1 kJ/mol of TMV subunit. The estimated proton release calculated from pressure-induced dissociation curves was 0.584 mol H(+)/mol of TMV subunit. These results suggest that the degree of virus inactivation by pressure and the immunogenicity of the inactivated structures can be optimized by modulating the surrounding pH.

An early tobacco mosaic virus-induced oxidative burst in tobacco indicates extracellular perception of the virus coat protein

Induction of reactive oxygen species (ROS) was observed within seconds of the addition of exogenous tobacco mosaic virus (TMV) to the outside of tobacco (Nicotiana tabacum cv Samsun NN, EN, or nn) epidermal cells. Cell death was correlated with ROS production. Infectivity of the TMV virus was not a prerequisite for this elicitation and isolated coat protein (CP) subunits could also elicit the fast oxidative burst. The rapid induction of ROS was prevented by both inhibitors of plant signal transduction and inhibitors of NAD(P)H oxidases, suggesting activation of a multi-step signal transduction pathway. Induction of intracellular ROS by TMV was detected in TMV-resistant and -susceptible tobacco cultivars isogenic for the N allele. The burst was also detected with strains of virus that either elicit (ToMV) or fail to elicit (TMV U1) N' gene-mediated responses. Hence, early ROS generation is independent or upstream of known genetic systems in tobacco that can mediate hypersensitive responses. Analysis of other viruses and TMV CP mutants showed marked differences in their ability to induce ROS showing specificity of the response. Thus, initial TMV-plant cell interactions that lead to early ROS induction occur outside the plasma membrane in an event requiring specific CP epitopes.

Differences of reconstitution process between tobacco mosaic virus and cucumber green mottle mosaic virus by synchrotron small angle X-ray scattering using low-temperature quenching

The differences of the reconstitution process of tobacco mosaic virus (TMV) and its mutant, cucumber green mottle mosaic virus (CGMMV) were investigated by the solution X-ray scattering measurements with the synchrotron radiation source using low-temperature quenching. The reconstitution in an aqueous solution is completely stopped below 5 degrees C. The TMV and CGMMV assembly was traced by the small-angle X-ray scattering (SAXS) measurements at 5 degrees C on a series of solutions prepared by low-temperature quenching after incubation at 20 degrees C for an appropriate interval between 0 and 60 min. The SAXS results were analyzed by the Guinier plot, the Kratky plot and the distance distribution function. The incubation of RNA and protein of CGMMV did not reconstitute at the initial reaction stages below 5 min and then began to reconstitute gradually. After 60 min, the radius of gyration for CGMMV reconstitution process reached almost the value for the initial stage of TMV reconstitution process. This is due to the fact the formation of double-layered disk in CGMMV protein is much slower than in TMV protein.

Historical overview of research on the tobacco mosaic virus genome: genome organization, infectivity and gene manipulation

Early in the development of molecular biology, TMV RNA was widely used as a mRNA [corrected] that could be purified easily, and it contributed much to research on protein synthesis. Also, in the early stages of elucidation of the genetic code, artificially produced TMV mutants were widely used and provided the first proof that the genetic code was non-overlapping. In 1982, Goelet et al. determined the complete TMV RNA base sequence of 6395 nucleotides. The four genes (130K, 180K, 30K and coat protein) could then be mapped at precise locations in the TMV genome. Furthermore it had become clear, a little earlier, that genes located internally in the genome were expressed via subgenomic mRNAs. The initiation site for assembly of TMV particles was also determined. However, although TMV contributed so much at the beginning of the development of molecular biology, its influence was replaced by that of Escherichia coli and its phages in the next phase. As recombinant DNA technology developed in the 1980s, RNA virus research became more detached from the frontier of molecular biology. To recover from this setback, a gene-manipulation system was needed for RNA viruses. In 1986, two such systems were developed for TMV, using full-length cDNA clones, by Dawson's group and by Okada's group. Thus, reverse genetics could be used to elucidate the basic functions of all proteins encoded by the TMV genome. Identification of the function of the 30K protein was especially important because it was the first evidence that a plant virus possesses a cell-to-cell movement function. Many other plant viruses have since been found to encode comparable 'movement proteins'. TMV thus became the first plant virus for which structures and functions were known for all its genes. At the birth of molecular plant pathology, TMV became a leader again. TMV has also played pioneering roles in many other fields. TMV was the first virus for which the amino acid sequence of the coat protein was determined and first virus for which cotranslational disassembly was demonstrated both in vivo and in vitro. It was the first virus for which activation of a resistance gene in a host plant was related to the molecular specificity of a product of a viral gene. Also, in the field of plant biotechnology, TMV vectors are among the most promising. Thus, for the 100 years since Beijerinck's work, TMV research has consistently played a leading role in opening up new areas of study, not only in plant pathology, but also in virology, biochemistry, molecular biology, RNA genetics and biotechnology.

Structure of ribgrass mosaic virus at 2.9 A resolution: evolution and taxonomy of tobamoviruses

Ribgrass mosaic virus (RMV) is a member of the tobamovirus group of plant viruses. The structure has been determined at 2.9 A resolution by fiber diffraction methods, and refined by molecular dynamics methods to an R-factor of 0.095. The carboxyl-carboxylate interactions that drive disassembly in tobamoviruses are present in RMV, but are very different from those in other tobamoviruses. RMV has some of the structural features of a subgroup I tobamovirus, a smaller number from subgroup II, and a number that appear to be unique to the RMV cluster of viruses. The structural studies confirm the evolutionary and taxonomic separation of the RMV cluster from both subgroup I and subgroup II tobamoviruses.

Structural analysis of A-protein of cucumber green mottle mosaic virus and tobacco mosaic virus by synchrotron small-angle X-ray scattering

The size and shape of A-protein of tobacco mosaic virus coat protein (TMVP) and cucumber green mottle mosaic virus coat protein (CGMMVP) were evaluated by means of small-angle X-ray scattering (SAXS) using a synchrotron radiation source, complemented by electron microscopic observations. The results imply that TMV and CGMMV A-proteins are composed of three and two subunits, respectively, stacked in the shape of an isosceles triangular prism at lower ionic strength. Considering the difference of the A-protein structure at higher and lower ionic strength, the globular core structure was proposed as a subunit which might be modeled as a thin isosceles triangular prism composed of four globular cores joined by rather flexible segments. These cores correspond probably to four helical regions in a subunit, and rearrange their relative positions according to the external conditions. A slight rearrangement of core positions in a subunit may result in the formation of A-proteins of various shapes.

Sequence analysis of the 3' termini of RNA1 and RNA2 of blueberry leaf mottle virus

The 3' termini of RNA1 and RNA2 of blueberry leaf mottle virus (BBLMV) were cloned and the cDNA sequence of a portion of the putative polymerase gene, the complete coat protein (CP) gene, and the 3' non-coding regions was determined. The N terminus of the coat protein gene was precisely located by comparison with the amino acid sequence determined by the Edman degradation sequencing of the purified coat protein. The coat protein gene encoded a polypeptide of 521 amino acids with a predicted M(r) of 57,542. Homology to BBLMV coat protein was highest with tomato ringspot virus (TomRSV) and cherry leaf roll virus (CLRV); two other nepoviruses also belonging to a sub-group defined by the presence of large RNA2 components. The 3' terminal 1390 nt of RNA1 and RNA2 were nearly identical and apparently non-coding. No statistically significant sequence homology was found between the 3' non-coding region of this length is unusual, but has been reported for two other related viruses, TomRSV and CLRV. The biological function of the long 3' non-coding region and how the high level of sequence homology is maintained between RNA1 and RNA2, is unknown. Possible mechanisms for conservation of the 3' terminus are discussed.

The nucleotide sequence of the coat protein genes and 3' non-coding regions of two resistance-breaking tobamoviruses in pepper shows that they are different viruses

The nucleotide sequence of the coat protein genes and 3' non-coding regions of two different resistance-breaking tobamoviruses in pepper have been determined. The deduced coat protein of an Italian isolate of pepper mild mottle virus (PMMV-I) consists of 156 amino acids and its 3' non-coding region is 198 nucleotides long. They have been found to be very similar in sequence and structure to those previously reported for a Spanish isolate (PMMV-S). In contrast, a Dutch isolate termed P 11 codes for a coat protein of 160 amino acids and its 3' non-coding region is 291 nucleotides long, which may have arisen by duplication. The nucleotide and the predicted coat protein amino acid sequence analysis show that this isolate should be considered as a new virus within the tobamovirus group. The term paprika mild mottle virus (PaMMV) is proposed.

Structure of the U2 strain of tobacco mosaic virus refined at 3.5 A resolution using X-ray fiber diffraction

The structure of the U2 strain of tobacco mosaic virus (TMV) has been determined by fiber diffraction methods at 3.5 A resolution, and refined by a combination of restrained least-squares and molecular dynamics methods to an R-factor of 0.096. The structure is extremely similar to that of the common strain of TMV, with the largest differences being in the protein loop that makes up the inner surface of the virus, and in the C-terminal region on the outer surface. Differences in the inner loop can be correlated with differences in the properties of the two viruses.

Biological activities of hybrid RNAs generated by 3'-end exchanges between tobacco mosaic and brome mosaic viruses

Sequences within the conserved, aminoacylatable 3' noncoding regions of brome mosaic virus (BMV) genomic RNAs 1, 2, and 3 direct initiation of negative-strand synthesis by BMV polymerase extracts and, like sequences at the structurally divergent but aminoacylatable 3' end of tobacco mosaic virus (TMV) RNA, are required in cis for RNA replication in vivo. A series of chimeric RNAs in which selected 3' segments were exchanged between the tyrosine-accepting BMV and histidine-accepting TMV RNAs were constructed and their amplification was examined in protoplasts inoculated with or without other BMV and TMV RNAs. TMV derivatives whose 3' noncoding region was replaced by sequences from BMV RNA3 were independently replication competent when the genes for the TMV 130,000-M(r) and 180,000-M(r) replication factors remained intact. TMV replicase can thus utilize the BMV-derived 3' end, though at lower efficiency than the wild-type (wt) TMV 3' end. Providing functional BMV RNA replicase by coinoculation with BMV genomic RNAs 1 and 2 did not improve the amplification of these hybrid genomic RNAs. By contrast, BMV RNA3 derivatives carrying the 3' noncoding region of TMV were not amplified when coinoculated with wt BMV RNA1 and RNA2, wt TMV RNA, or all three. Thus, BMV replicase appeared to be unable to utilize the TMV 3' end, and there was no evidence of intervirus complementation in the replication of any of the hybrid RNAs. In protoplasts coinoculated with BMV RNA1 and RNA2, the nonamplifiable RNA3 derivatives bearing TMV 3' sequences gave rise to diverse new rearranged or recombined RNA species that were amplifiable.

Odontoglossum ringspot virus coat protein: sequence and antigenic comparisons with other tobamoviruses

Comparative immunochemical analysis of different tobamoviruses indicated that the previously reported coat protein sequence of Odontoglossum ringspot virus was likely erroneous. This sequence has been determined again by direct sequencing of the genomic RNA and was found to differ from the previously proposed sequence in 31 of the 157 amino acid residues. The extent of antigenic cross-reactivity between ORSV protein and other tobamovirus proteins was measured by ELISA and found to correlate satisfactorily with the degree of sequence homology.

The complete nucleotide sequence of the genomic RNA of the tobamovirus tobacco mild green mosaic virus

The complete nucleotide sequence of the genomic RNA of the tobamovirus tobacco mild green mosaic virus (TM-GMV) was determined. It shows 64.4% sequence homology with the genomic RNA of tobacco mosaic virus (TMV) and 66.0% with that of tomato mosaic virus (ToMV). Its genomic organization is similar to that of TMV and ToMV. The 5' proximal open reading frame (ORF) encodes a 126K polypeptide and a 183K readthrough product in which nucleotide-binding and polymerase-sequence motifs are found. The third ORF encodes a 28.5K protein homologous to TMV and ToMV movement proteins. A conserved core is found with four other tobamoviruses and two tobraviruses suggesting a common mechanism of cell-to-cell movement for tobamo- and tobraviruses. The fourth ORF encodes the 17.5K coat protein. Homology between the RNAs of TMGMV and its satellite virus STMV is limited to their 3' termini, and structural comparisons suggest that this region may determine the nature of the satellite/helper virus interaction.

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.

Similarities among plant virus (+) and (-) RNA termini imply a common ancestry with promoters of eukaryotic tRNAs

The 5' ends of brome mosaic virus (BMV) RNAs contain sequences similar to the consensus internal control region (ICR) of pol III promoters in tRNA genes. Comparison of BMV (+)RNA 5' termini with BMV (-)RNA termini revealed the presence of two (tandem) repeats of some 30 nucleotides, the more internal containing a region of 73% similarity to the tRNA consensus ICR2 (downstream) region of the ICR. Tandem repeats containing motifs similar to the ICR2 consensus were found at the 5' termini of (-)RNAs of cucumo-, tobamo-, and tymoviruses whose 3' (+)RNAs have aminoacylatable tRNA-like structures. Single regions of homology to the BMV(+)RNA 5' terminus, containing an ICR2-like motif, were detected for several tobravirus RNAs, and for satellite tobacco necrosis virus RNA. The (+)-stranded genomes of these viruses have not been shown to be capable of amino acid esterification. The ICR2 consensus (GGUUCGANUCC) is nearly palindromic, and is contained with the T psi C loop of tRNAs and viral analogs. Consequently, tRNA promoter-like motifs can be seen at both termini of (+) and (-) RNAs of bromoviruses and other viruses. The presence of ICR1 and ICR2-like sequences in BMV genomic 5' (+)RNAs and the tobamovirus 5' (-)RNAs may reflect promoter arrangements of primordial genomic RNAs ancestral to both modern plant viruses and eukaryotic tRNAs. Several derivative concepts related to genome evolution are discussed, including the origin of asymmetric strand synthesis of RNAs.

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

The TMV-encoded 30-kDa protein has been implicated in the cell-to-cell transport of TMV in the infected plant. The polyethylene glycol-mediated inoculation of tobacco protoplasts with TMV particles and TMV RNA was used to compare the time courses of the viral 30-kDa protein synthesis in vivo. Upon infection of protoplasts with TMV RNA, the synthesis of the viral 30-kDa protein starts after 4 to 6 hr, has its maximum after 8 to 10 hr, and decreases. After inoculation of protoplasts with TMV, however, the start of the viral 30-kDa protein synthesis and its maximum are delayed by 2 hr, followed by the same decrease. We show that actinomycin D dramatically stimulates the synthesis of the 30-kDa protein by up to 2 orders of magnitude, whereas the synthesis of the viral 126 kDa, the 183 kDa, and the coat protein is increased only by a factor of 2. Surprisingly, actinomycin V is twice as active as actinomycin D, whereas actinomycin I is nearly inactive. The specific stimulation of the 30-kDa synthesis by actinomycin D in vivo depends neither on the Nicotiana variety nor on the TMV strain used. Final evidence that the 30-kDa protein is truly TMV-derived is provided by the slightly different electrophoretic mobilities of the 30-kDa proteins encoded by TMV strains vulgare, dahlemense, and U2. The identification of the 30-kDa protein in two-dimensional gels was achieved for the first time by a combination of ionic and nonionic detergents for the solubilization of the 30-kDa protein and by the specific stimulation of its synthesis by actinomycin D. The mechanism of the strong and selective actinomycin effect on the viral 30-kDa protein synthesis in vivo is as yet obscure. Actinomycin does not appear to act directly on viral protein biosynthesis, since it neither stimulates the 30-kDa synthesis upon translation of TMV RNA in vitro nor alters the ratio of the products. Actinomycin may rather act by inhibiting selectively the synthesis of a host factor whose synthesis starts at least 4 hr after TMV infection and which strongly inhibits the expression of the viral 30-kDa transport protein.

Sequence and structure at the genome 3' end of the U2-strain of tobacco mosaic virus, a histidine-accepting tobamovirus

The primary sequence of the 3' noncoding region of U2-TMV RNA was determined. A structural model was proposed based on chemical and enzymatic structure mapping as well as on analyses of nuclease protection by aminoacyl-tRNA-synthetase. The model agrees with those proposed for TMV "vulgare" RNA and confirms their general validity for the tobamoviruses. The RNA appears to have a tRNA-like, L-shaped structure at the 3' terminus, linked to a quasi-continuous double-helical stalk, with five pseudoknots involved in the formation of the whole structure. However, the structure of U2-TMV RNA is less stringently conserved than the 3' termini of "vulgare" and other histidine-accepting tobamoviruses. This difference is reflected in the kinetics of aminoacylation of the RNA.

The tobacco mosaic virus assembly origin RNA. Functional characteristics defined by directed mutagenesis

The in vitro reassembly of tobacco mosaic virus (TMV) begins with the specific recognition by the viral coat protein disk aggregate of an internal TMV RNA sequence, known as the assembly origin (Oa). This RNA sequence contains a putative stem-loop structure (loop 1), believed to be the target for disk binding in assembly initiation, which has the characteristic sequence AAGAAGUCG exposed as a single strand at its apex. We show that a 75-base RNA sequence encompassing loop 1 is sufficient to direct the encapsidation by TMV coat protein disks of a heterologous RNA fragment. This RNA sequence and structure, which is sufficient to elicit TMV assembly in vitro, was explored by site-directed mutagenesis. Structure analysis of the RNA identified mutations that appear to effect assembly via a perturbation in RNA structure, rather than by a direct effect on coat protein binding. The binding of the loop 1 apex RNA sequence to coat protein disks was shown to be due primarily to its regularly repeated G residues. Sequences such as (UUG)3 and (GUG)3 are equally effective at initiating assembly, indicating that the other bases are less functionally constrained. However, substitution of the sequences (CCG)3, (CUG)3 or (UCG)3 reduced the assembly initiation rate, indicating that C residues are unfavourable for assembly. Two additional RNA sequences within the 75-base Oa sequence, both of the form (NNG)3, may play subsidiary roles in disk binding. RNA structure plays an important part in permitting selective protein-RNA recognition, since altering the RNA folding close to the apex of the loop 1 stem reduces the rate of disk binding, as does shortening the stem itself. Whereas the RNA sequence making up the hairpin does not in general affect the specificity of the protein-RNA interaction, it is required to present the apex signal sequence in a special conformation. Mechanisms for this are discussed.

Replication of chimeric tobacco mosaic viruses which carry heterologous combinations of replicase genes and 3' noncoding regions

Three tobacco mosaic virus (TMV)-L (tomato strain)-derived chimeras, designated OL1, LG11, or LK31, were constructed by replacing the 3' noncoding region with the corresponding sequence of TMV-OM (common strain), cucumber green mottle mosaic virus (CGMMV), or TMV-Cc (cowpea strain), respectively. The genomic RNAs of TMV-L, -OM, and CGMMV carry histidine-accepting tRNA-like structures at their 3' termini, while the genome of TMV-Cc accepts valine. The three chimeric viruses were able to multiply in both tobacco protoplasts and plants. Multiplication of OL1 in protoplasts was similar to that of the parental strain, L, but in the cases of LG11 and LK31 multiplication was decreased. Sequence analyses of progeny RNAs revealed that viruses with chimeric sequences propagated. These data suggested that TMV-L replicase recognizes the 3' terminal structures of TMV-OM, CGMMV, and TMV-Cc and can initiate minus-strand RNA synthesis. The relationship between the virus-coded component(s) of TMV replicase and the 3' terminal region may not be so stringent.

Preliminary X-ray fiber diffraction studies of cucumber green mottle mosaic virus, watermelon strain

Fiber diffraction patterns have been obtained for cucumber green mottle mosaic virus, watermelon strain (a distant relative of tobacco mosaic virus), and two heavy-atom derivatives. These patterns and the similarity between the cucumber and the tobacco virus offer the potential of a full structure determination of the cucumber virus.

Correlation of co-ordinated amino acid substitutions with function in viruses related to tobacco mosaic virus

Sequence data are available for the coat proteins of seven tobamoviruses, with homologies ranging from at least 26% to 82%, and atomic co-ordinates are known for tobacco mosaic virus (TMV) vulgare. A significant spatial relationship has been found between groups of residues with identical amino acid substitution patterns. This strongly suggest that their location is linked to a particular function, at least in viruses identical with the wild-type for these residues. The most conserved feature of TMV is the RNA binding region. Core residues are conserved in all viruses or show mutations complementary in volume. The specificity of inter-subunit contacts is achieved in different ways in the three more distantly related viruses.

Tobacco mosaic virus coat protein and the large subunit of the host protein ribulose-1,5-biphosphate carboxylase share a common antigenic determinant

An immunological relationship was detected between the coat protein of the common (U1) strain of tobacco mosaic virus (TMV) and the large subunit of the ubiquitous CO2-fixing host enzyme, ribulose-1,5-biphosphate carboxylase (RuBisCo). When assayed by Western immunoblotting or indirect ELISA, polyclonal antisera to TMV coat protein and to RuBisCo reacted with both antigens. In addition, a monoclonal antibody specific for the C-terminal antigenic determinant of TMV coat protein reacted with RuBisCo. Conversely, several monoclonal antibodies generated to the large subunit of RuBisCo reacted with TMV coat protein. This cross-reactivity was verified by an examination of the amino acid sequences of both proteins. A region of homology was found between the carboxy proximal portion of coat protein and the sequence 60-73 residues from the amino terminus of RuBisCo large subunit. This homology was not mirrored at the nucleic acid level because of different codon usages for the two proteins.

Regulation of protein synthesis in virus-infected animal cells

This chapter summarizes the structural features that govern the translation of viral mRNAs: where the synthesis of a protein starts and ends, how many proteins can be produced from one mRNA, and how efficiently. It focuses on the interplay between viral and cellular mRNAs and the translational machinery. That interplay, together with the intrinsic structure of viral mRNAs, determines the patterns of translation in infected cells. It also points out some possibilities for translational regulation that can only be glimpsed at present, but are likely to come into focus in the future. The mechanism of selecting the initiation site for protein synthesis appears to follow a single formula. The translational machinery displays a certain flexibility that is exploited more frequently by viral than by cellular mRNAs. Although some of the parameters that determine efficiency have been identified, how efficiently a given mRNA will be translated cannot be predicted by summing the known parameters.

Translational interference at overlapping reading frames in prokaryotic messenger RNA

In overlapping reading frames of prokaryotic mRNA, the ribosome-binding site (RBS) of the downstream cistron is part of the coding sequence of the upstream message. We have examined whether the rate of translation in Escherichia coli can be sufficiently high to preclude the use of an RBS in initiation of protein synthesis when it is part of an actively decoded reading frame. The two sets of gene overlap present in the RNA phage MS2 are used as a model system. We find that translation of an upstream cistron can fully block initiation of protein synthesis at the overlapping RBS of the downstream cistron. Nonsense mutations in the upstream gene restore the translation of the downstream gene.

Detection of distant antigenic relationships between insect and bird lysozymes by ELISA

We used an indirect enzyme-linked immunosorbent assay (ELISA) for measuring the immunological cross-reactivities between bird lysozymes and a lysozyme isolated from the blood of the insect Locusta migratoria. The degrees of cross-reactivity among five avian lysozymes measured by ELISA agreed approximately with those observed in earlier work using microcomplement fixation tests. This latter technique is not suitable for detecting immunological cross-reactivity between proteins that differ in sequence by more than 30%-40%. In contrast, ELISA is able to detect distant relationships between antigens such as lysozymes that differ in sequence by as much as 60%. It seems likely that the use of ELISA procedures will extend the range of homologous proteins that can be compared by immunochemical means.

Single amino acid substitution in 30K protein of TMV defective in virus transport function

Involvement of the tobacco mosaic virus (TMV) coded 30K protein in a virus transport function within the infected plant has been suggested. Previously a temperature sensitive mutant, TMV Ls 1, that is defective in cell-to-cell movement at a restrictive temperature, was reported. To demonstrate a relationship between the 30K protein and the transport function, the nucleotide sequences of the 30K and coat protein cistrons of the mutant, TMV Ls 1, and the wild type, TMV L (tomato strain) were compared. A single base substitution which causes replacement of a proline codon in the L strain by a serine codon was found in the Ls 1 mutant. Results support the notion that the 30K protein is responsible for the virus transport function.