Nucleotide sequence at the 5' extremity of tobacco-mosaic-virus RNA. 2. The coding region (nucleotides 69-236)

Functions of the 5'- and 3'-untranslated regions of tobamovirus RNA

The tobamovirus genome is a 5'-m(7)G-capped RNA that carries a tRNA-like structure at its 3'-terminus. The genomic RNA serves as the template for both translation and negative-strand RNA synthesis. The 5'- and 3'-untranslated regions (UTRs) of the genomic RNA contain elements that enhance translation, and the 3'-UTR also contains the elements necessary for the initiation of negative-strand RNA synthesis. Recent studies using a cell-free viral RNA translation-replication system revealed that a 70-nucleotide region containing a part of the 5'-UTR is bound cotranslationally by tobacco mosaic virus (TMV) replication proteins translated from the genomic RNA and that the binding leads the genomic RNA to RNA replication pathway. This mechanism explains the cis-preferential replication of TMV by the replication proteins. The binding also inhibits further translation to avoid a fatal ribosome-RNA polymerase collision, which might arise if translation and negative-strand synthesis occur simultaneously on a single genomic RNA molecule. Therefore, the 5'- and 3'-UTRs play multiple important roles in the life cycle of tobamovirus.

Nucleotide sequence at the 5' extremity of turnip yellow mosaic virus genome RNA

The sequence of the first 110 nucleotides at the 5' extremity of turnip yellow mosaic virus genome RNA has been determined. The sequence is blocked at its 5' terminus with the group pppm(7)G and contains two AUG triplets. The determined sequence bears a strong resemblance to the 5' noncoding region of rabbit beta-globin mRNA. Region 95-103 of the sequence can base-pair with part of the 3' extremity of either the genome RNA or the coat protein mRNA.

Deletion analysis of the 5' untranslated leader sequence of tobacco mosaic virus RNA

To determine the sequences essential for viral multiplication in the 5' untranslated leader sequence of tobacco mosaic virus RNA, mutant TMV-L (a tomato strain) RNAs which carry several deletions in this 71-nucleotide sequence were constructed by an in vitro transcription system and their multiplication was analyzed by introducing mutant RNA into tobacco protoplasts by electroporation. Large deletions of the sequence from nucleotides 9 to 47 or 25 to 71 abolished viral multiplication; when about 10-nucleotide deletions were introduced throughout this 5' leader sequence, only deletion of the sequence from nucleotides 2 to 8 abolished detectable viral multiplication. This mutant RNA, however, directed the synthesis of the 130,000-molecular-weight protein in a rabbit reticulocyte lysate in vitro translation system, and consequently this 5'-proximal portion appears likely to be essential for replication.

Methods for cDNA cloning and sequencing tobacco mosaic virus RNA

DNA complementary to tobacco mosaic virus (TMV) RNA (cDNA) was prepared by priming reverse transcription with synthetic oligonucleotides. The cDNAs terminated prematurely at many specific sites and no transcripts longer than about 2000 nucleotides were obtained. However, the entire 6395 nucleotide long TMV RNA could be copied into cDNA by specific priming with a series of 13 to 17 residue long oligonucleotides or by non-specific priming with short, 4 to 7 residue, oligonucleotides. A number of different priming methods were used to convert the cDNA into double-stranded DNA (dsDNA). The double-stranded cDNA was recovered by shotgun cloning into M13 and analysed by sequencing. The frequency at which cDNA clones were recovered has been used to compare various cDNA cloning strategies.

Multiple ribosome binding to the 5'-terminal leader sequence of tobacco mosaic virus RNA. Assembly of an 80S ribosome X mRNA complex at the AUU codon

Tobacco mosaic virus (TMV) RNA with a long 5'-terminal leader sequence, as well as its isolated leader fragment (called omega), can form disome initiation complexes with wheat germ ribosomes. The second ribosome of the disome complex is bound to the leader sequence, upstream of an 80S particle occupying the AUG-containing initiation site [ Filipowicz and Haenni (1979) Proc. Natl Acad. Sci. USA 76, 3111-3115; Konarska et al. (1981) Eur. J. Biochem. 114, 221-227]. In order to identify the parts of omega important for interaction with ribosomes, the 5'-terminally-labelled omega was treated with alkali and the resultant fragments of different lengths were used in binding experiments. A 16-nucleotide-long fragment bearing the AUU sequence at the 3' end is the shortest oligonucleotide capable of forming 80S complexes with wheat germ ribosomes. Full-length (73 nucleotides) omega with AUG at the 3' terminus is the only RNA fragment supporting disome complex formation. Synthetic oligoribonucleotides were prepared for a study of 80S complex assembly at codons other than AUG. Hexadecanucleotide (A) 13A -U-U and, to lesser extent, also (A) 13A -U-C, (A) 13A -U-A and (A) 13A -C-G bind 80S ribosomes. Formation of the (A) 13A -U-U X 80S complex is dependent on the presence of initiator Met- tRNAMerf . Assembly of the 80S particle at the AUU sequence is not an artifact resulting from the terminal position of this triplet. (A) 13A -U-U elongated with over 100 A residues still efficiently binds an 80S ribosome positioned, as established by ribosome protection experiments, at the AUU triplet. The present results support the notion that 80S initiation-like complexes can be formed at sequences containing AUU codons. The possible function of these complexes as intermediates in initiation of translation of some viral RNAs is discussed.

The 5'-terminal sequence of TMV RNA. Question on the polymorphism found in vulgare strain

The complete nucleotide sequence of TMV RNA (common strain) reported in [Proc. Natl. Acad. Sci. USA (1982) 79, 5818] its 5'-end to be represented by two variants which differed in length. We have tested that result and sequenced the 5'-terminal regions of two strains of TMV RNA (common strain OM and tomato strain L) using cloned cDNA copies. The results showed that the 5'-terminal region of the TMV genome is not polymorphic and that one of the two variants cited above represents a tomato strain but not the common strain.

Nucleotide sequence of tobacco mosaic virus RNA

Oligonucleotide primers have been used to generate a cDNA library covering the entire tobacco mosaic virus (TMV) RNA sequence. Analysis of these clones has enabled us to complete the viral RNA sequence and to study its variability within a viral population. The positive strand coding sequence starts 69 nucleotides from the 5' end with a reading frame for a protein of Mr 125,941 and terminates with UAG. Readthrough of this terminator would give rise to a protein of Mr 183,253. Overlapping the terminal five codons of this readthrough reading frame is a second reading frame coding for a protein of Mr 29,987. This gene terminates two nucleotides before the initiator codon of the coat protein gene. Potential signal sequences responsible for the capping and synthesis of the coat protein and Mr 29,987 protein mRNAs have been identified. Similar sequences within these reading frames may be used in the expression of sets of proteins that share COOH-terminal sequences.

Codon binding and translational properties of an isoaccepting lysine tRNA peculiar to virus-transformed Cells

Isoaccepting lysyl-tRNAs from virus-transformed cells in culture were fractionated in the RPC-5 system into peaks 1, 2, 4, 5a, 5, and 6. tRNALys6 previously was found predominantly associated with transformed cells. The codon response of each peak was determined in an E. coli ribosomal binding assay. tRNALys1, tRNALys2, and tRNALys4 are highly specific for the 5'AAG3' codon. tRNALys5 and tRNALys5a preferentially bind in response to AAA. tRNALys6 binds in response to AAA 3-fold better than in response to AAG. The presence of thiolated nucleosides in the anticodon regions of tRNALys5a, tRNALys5, and tRNALys6 is indicated by I2-inactivation of aminoacylation ability with no effect on the other is isoacceptors. Functional abilities of the isoacceptors were compared in a wheat germ translational system with tobacco mosaic virus RNA as messenger. All of the isoacceptors function about equally well in translation except for tRNALys6, which is only 14 to 24% as effective as the other isoacceptors.

Binding of ribosomes to linear and circular forms of the 5'-terminal leader fragment of tobacco-mosaic-virus RNA

The sequence of the 5'-terminal leader fragment preceding the AUG codon in the RNA of tobacco mosaic virus (TMV), tomato strain, SPS isolate, has been determined. This RNA, similarly to the RNAs of the U1 and Dahlemense strains of TMV [Kukla et al. (1979) Eur. J. Biochem. 98, 61--66] has the 7-methylguanosine(5')triphospho(5')guanosine cap separated from the initiation codon by a long stretch of nucleotides devoid of guanosine residues. The RNase-T1-resistant 73-nucleotide-long leader fragment of TMV RNA from the SPS isolate was assayed for its ability to interact with eukaryotic and prokaryotic ribosomes. The linear fragment, labelled either at its 5' or 3' end, efficiently formed disome initiation complexes when incubated with wheat-germ protein-synthesis extract. In contrast to its linear counterpart, the circular covalently closed RNA leader fragment, obtained in a reaction catalysed by T4 RNA ligase, was unable to interact with wheat germ ribosomes. Both kinds of leader fragment bound equally well to Escherichia coli 70-S ribosomes. The results offer further support to the notion that in eukaryotic initiation the free 5' end (either capped or uncapped) is required for mRNA interaction with ribosomes. Furthermore, they suggest that both ribosomes found in disome initiation complexes with the TMV RNA leader fragment enter the mRNA sequentially via the free 5' terminus.

Codon frequencies in 119 individual genes confirm consistent choices of degenerate bases according to genome type

The poor printing of our previous Figure 2 (1) is corrected. Codon usage in mRNA sequences just published is also given. A new correspondence analysis is done, based on simultaneous comparison in all mRNA of use of the 61 codons. This analysis reinforces our claim that most genes in a genome, or genome type, have the same coding strategy; that is, they show similar choices among synonymous codons, or among degenerate bases (2). Like analysis on frequency variation in the amino acids coded reveals an entirely different pattern.

Codon catalog usage and the genome hypothesis

Frequencies for each of the 61 amino acid codons have been determined in every published mRNA sequence of 50 or more codons. The frequencies are shown for each kind of genome and for each individual gene. A surprising consistency of choices exists among genes of the same or similar genomes. Thus each genome, or kind of genome, appears to possess a "system" for choosing between codons. Frameshift genes, however, have widely different choice strategies from normal genes. Our work indicates that the main factors distinguishing between mRNA sequences relate to choices among degenerate bases. These systematic third base choices can therefore be used to establish a new kind of genetic distance, which reflects differences in coding strategy. The choice patterns we find seem compatible with the idea that the genome and not the individual gene is the unit of selection. Each gene in a genome tends to conform to its species' usage of the codon catalog; this is our genome hypothesis.

Characterization of long guanosine-free RNA sequences from the Dahlemense and U2 strains of tobacco mosaic virus

Four naturally occurring strains of tobacco mosaic virus, U2, Dahlemense, CV4, and the bean form of tobacco mosaic virus, were tested for the existence of long T1 RNAase oligonucleotides analogous to the oligonucleotide omega found in the common or U1 strain of tobacco mosaic virus and which makes up the 5' non-coding region of the RNA molecule. U2 and Dahlemense RNA were each found to contain this type of long T1 RNAase oligonucleotide with chain lengths of 54 and 74--77 residues, respectively. The sequence of the two oligonucleotides was determined mostly by using 5'-32P-labelled material in vitro and rapid polyacrylamide gel sequencing techniques.

Nucleotide sequence at the 5' extremity of tobacco-mosaic-virus RNA. 1. The noncoding region (nucleotides 1-68)

The sequence of the 5' noncoding region of tobacco mosaic virus RNA has been determined. The noncoding region is 68 nucleotides long and is unusual in that it contains no internal guanosine residues. The long T1 oligonucleotide containing the guanosine-free tract was isolated from a T1 ribonuclease digest of tobacco mosaic virus RNA and sequenced by labelling techniques in vitro using polynucleotide kinase. The guanosine-free tract is terminated by the first potential initiation codon in the RNA molecule and several lines of evidence suggest that this AUG triplet is operational in initiating viral protein synthesis (see following paper). The 5'-noncoding region cannot base-pair extensively with the 3'-terminal sequence of 18-S ribosomal RNA from rabbit reticulocytes.