Genome structure of tobacco necrosis virus strain A

An almost complete sequence of the RNA genome of tobacco necrosis virus (TNV) strain A has been determined. The genome organization is very similar to that of carnation mottle virus (CarMV) and turnip crinkle virus (TCV). The 5'-proximal open reading frame (ORF) encodes a 23-kDa protein and read-through of its amber codon into the second ORF is presumably used for the translation of a 82-kDa protein. The third large ORF encodes the 30-kDa coat protein. Two small ORFs are located upstream and one immediately downstream of this coat protein cistron. Extensive sequence similarity was found between the TNV 82-kDa protein and the putative polymerases of TCV, CarMV, cucumber necrosis virus (CNV), maize chlorotic mottle virus (MCMV), red clover necrotic mosaic virus (RCNMV), and barley yellow dwarf virus (BYDV). The TNV coat protein is very similar to southern bean mosaic virus (SBMV) capsid protein. Of the predicted small proteins only a 7.9-kDa protein shows some sequence similarity with a corresponding protein of MCMV, CarMV, and TCV. The others are unique to TNV. Except for the first four nucleotides at the 5' end no homology was found with the RNA of STNV (satellite of TNV)

Intron-mediated enhancement of transgene expression in maize is a nuclear, gene-dependent process

In monocots, transgene expression can be stimulated by over two magnitudes by including an intron in the 5' untranslated region (UTR). The underlying mechanism is presently unknown. Inclusion of the salT intron into the 5' UTR of cat and bar genes stimulated expression of the first gene only, indicating that intron-mediated enhancement of expression (IME) is gene-dependent. Stimulation was associated with increased cat RNA levels, which did not result from a reduced cytoplasmic turnover and were not associated with increased translation. This implies that IME acts in the nucleus. importantly the cytoplasmic accumulation of spliced cat transcripts, even with IME, is less than that encoded by the intronless bar gene. As the cat and bar genes were flanked by identical regulatory signals, and the transcripts had a similar cytoplasmic stability, it may mean that IME rescues rather than stimulates gene expression

The tobacco luminal binding protein is encoded by a multigene family

We have cloned cDNAs of the tobacco homolog of the luminal binding protein (BiP) that has been described in other higher eukaryotes. In contrast to the mammalian and yeast protein, tobacco BiP is encoded by a multigene family. The gene products of all the cloned members of this family contain a carboxy-terminal His-Asp-Glu-Leu peptide that may form the signal for retention in the endoplasmic reticulum. Analysis of expression patterns revealed that BiP transcripts are predominantly present in tissues with high rates of cell divisions, in secretory tissues, and in cells treated with tunicamycin. We also show that a chimeric gene containing the coding region of one of the tobacco BiP genes is able to complement a mutation in the Saccharomyces cerevisiae BiP gene

The functional organization of the octopine Agrobacterium tumefaciens plasmid pTiB6S3

We have used the transposon Tn7 to isolate insertion and deletion mutations in the octopine Ti-plasmid pTiB6S3. Mutations that inactivate most of the known Ti phenotypes have been located on the physical map. Most importantly, we have positioned several regions involved in the determination of oncogenicity. They correspond to homology regions between octopine and nopaline plasmids. One of these regions, the T region, is part of the Ti-plasmid DNA present in transformed plant cells. Some Tn7 insertions in this region are weakly virulent and the tumor tissue, incited by these mutant Ti plasmids, readily produce proliferating shoots

Structure and expression analyses of the S-adenosylmethionine synthetase gene family in Arabidopsis thaliana

The plant, Arabidopsis thaliana, contains two S-adenosylmethionine synthetase-encoding genes (sam). Here, we analyze the structure and expression of the sam-2 gene and compare it with the previously described sam-1 gene. Northern-blot analysis using gene-specific probes shows that both sam-1 and sam-2 are highly expressed in stem, root, and callus tissue. This similar expression pattern might be mediated by the presence of three highly conserved sequences in the 5' region of both sam genes. Using a chimeric beta-glucuronidase (GUS)-encoding gene, we show that in transgenic tobacco plants, 748 bp of 5' sam-1 sequences generate high GUS activity in the same type of tissues as previously observed in transgenic A. thaliana plants. A deletion analysis of these 5' sam-1 sequences indicates that 224 bp of 5' sam-1 sequences can still induce higher expression of the gene in stem and root relative to leaf. However, the level of expression is reduced when compared to the expression level obtained with the full-length promoter