Effects of 5' flanking sequences and changes in the 5' internal control region on the transcription of rice tRNA % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaqcKbay-haafaqabe% GabaaabaGaae4raiaabYgacaqG5baabaGaae4raiaaboeacaqGdbaa% aaaa!3CC7!\[\begin{array}{*{20}c} {{\text{Gly}}} \\ {{\text{GCC}}} \\ \end{array} \]

The TATA motif, the CAA motif and the poly(T) transcription termination motif are all important for transcription re-initiation on plant tRNA genes

The effect of alteration of 5' and 3' flanking sequences on the transcription of plant tRNA genes was analysed using an RNA polymerase III-dependent in vitro transcription system derived from nuclei of cultured tobacco cells. A TATA-like sequence and the CAA motif frequently observed upstream of plant tRNA genes, and the poly(T) stretch usually present downstream, were shown to be necessary for efficient re-initiation of transcription. The CAA motif was shown to be a transcription initiation site. Introduction of the CAA and TATA-like motifs into a gene naturally lacking them greatly enhanced transcription by promoting efficient re-initiation.

PLANT IN VITRO TRANSCRIPTION SYSTEMS

▪ Abstract  In vitro transcription systems provide a powerful tool for detailed analysis of transcription reactions including initiation, elongation, and termination. Despite problems inherent to plant cells, efforts have been made to develop plant in vitro transcription systems in the past decade. These efforts have finally culminated in the development of reliable in vitro systems from suspension-cell cultures of both monocot and dicot plants. These systems can be useful in elucidating the specific mechanisms involved in the process of plant transcription and thus can potentially open a new era of transcription studies in plants.

Exercise and in vivo natural cytotoxicity against tumour cells of varying metastatic capacity

Identification of modifiable risk factors which contribute to tumour metastasis is an important goal of cancer prevention research. This study was designed to evaluate the role of moderate exercise conditioning on the in vivo retention of radiolabelled H-ras-transformed fibroblasts (CIRAS 1 and CIRAS 3 cell lines) in mice with (C3H/He-bg2J/+) and without (C3H/HeJ) the beige (bg) mutation which produces impaired natural killer (NK) cell function. Mice were randomly assigned to treadmill training (20 m/min, 30 min/day, 5 times/week) or remained sedentary for 9 weeks. C3H beige mice had significantly higher retention in the lungs of CIRAS 1 tumour cells (P < 0.0001) than genotypically normal C3H/HeJ mice. There was a significant main effect of exercise conditioning (P < 0.05) with trained mice (irrespective of genotype) having lower tumour retention (44 +/- 3%) than sedentary controls (53 +/- 3%). Comparing the in vivo retention of CIRAS 1 and CIRAS 3 in the lungs of genotypically normal mice, we observed higher retention of CIRAS 1 (48 +/- 2%, compared with 18 +/- 2% for CIRAS 3; P < 0.0001). There was a significant interaction effect of exercise and tumour type (P < 0.05); trained mice had a lower retention for CIRAS 1 than sedentary controls (43 +/- 3%, compared with 53 +/- 3%), while training status had no effect on CIRAS 3 retention. There were no significant differences in final tumour multiplicity in the lung as a function of exercise condition. The data suggest that exercise conditioning reduces some measures of in vivo burden but only for the less aggressive tumour variant (CIRAS 1); further, innate immune mechanisms other than NK cells are likely to be involved in this modest protective effect.

Tissue-specific and light-responsive regulation of the promoter region of the Arabidopsis thaliana chloroplast omega-3 fatty acid desaturase gene (FAD7)

The Arabidopsis FAD7 gene encodes a chloroplast omega-3 fatty acid desaturase that catalyzes the desaturation of lipid-linked dienoic fatty acids (18:2 and 16:2). An 825 bp FAD7 promoter fragment upstream from the transcriptional start point contained several short sequences which were homologous to the cis-elements (box II, G-box, etc.) conserved in many light-responsive genes. We introduced the FAD7 promoter fused to the beta-glucuronidase (GUS) or the luciferase (LUC) reporter gene into tobacco plants. The -825 promoter sequence conferred tissue-specific and light-responsive expression to both these reporter genes in transgenic tobacco, indicating that these expressions of the FAD7 gene were regulated mainly at the transcriptional level. Histochemical GUS staining showed that the activity of the FAD7 promoter is restricted to the tissues with chloroplast-containing cells although the staining was noticeably absent in the chloroplast-containing cells associated with vascular systems. The 5' deletion experiments of the promoter revealed that the -362/-166 region, containing two putative box II sequences, was responsible for the tissue-specific and light-responsive expression of the FAD7 gene.

Cloning of a cDNA encoding tobacco omega-3 fatty acid desaturase

A cDNA was isolated from a tobacco (Nicotiana tabacum cv. SR1) leaf cDNA library using, as a hybridization probe, a cDNA fragment from the gene (fad7) encoding Arabidopsis thaliana chloroplast omega-3 fatty acid (FA) desaturase. The deduced 379-amino-acid (aa) sequence has 67-71% identity to those deduced from the previously described genes encoding the omega-3 FA desaturases of A. thaliana. The absence of an N-terminal extension transit peptide in the deduced aa sequence of the cDNA clone and the accumulation pattern of the mRNA corresponding to this cDNA in leaf and root tissues indicate that the isolated cDNA encodes a tobacco microsomal omega-3 FA desaturase.

Transfer RNA-mediated suppression of stop codons in protoplasts and transgenic plants

We have developed a simple, rapid and sensitive assay for tRNA gene expression in plant cells. A plant tRNA(Leu) gene was site-specifically mutated to encode each of the three anticodon sequences (CUA, UUA and UCA) that recognize, respectively, the amber, ochre and opal stop codons. The suppression activity of these genes was detected by their ability to restore transient beta-glucuronidase (GUS) expression in tobacco protoplasts electroporated with GUS genes containing premature stop codons. Protoplasts co-electroporated with the amber suppressor tRNA gene and a GUS gene containing a premature amber stop codon showed up to 20-25% of the activity found in protoplasts transfected with the functional control GUS gene. Ochre and opal suppressors presented maximum efficiencies of less than 1%. This system could be adapted to examine transcription, processing or aminoacylation of tRNAs in plant cells. In addition, phenotypically normal, fertile tobacco plants expressing a stably incorporated amber suppressor tRNA gene have been obtained. This suppressor tRNA can be used to transactivate a target gene containing a premature amber stop codon by a factor of at least several hundred-fold.

The tRNA(Tyr) multigene family of Nicotiana rustica: genome organization, sequence analyses and expression in vitro

Tobacco tRNA(Tyr) genes are mainly organized as a dispersed multigene family as shown by hybridization with a tRNA(Tyr)-specific probe to Southern blots of Eco RI-digested DNA. A Nicotiana genomic library was prepared by Eco RI digestion of nuclear DNA, ligation of the fragments into the vector lambda gtWES.lambda B and in vitro packaging. The phage library was screened with a 5'-labelled synthetic oligonucleotide complementary to nucleotides 18 to 37 of cytoplasmic tobacco tRNA(Tyr). Eleven hybridizing Eco RI fragments ranging in size from 1.7 to 7.5 kb were isolated from recombinant lambda phage and subcloned into pUC19 plasmid. Four of the sequenced tRNA(Tyr) genes code for the known tobacco tRNA1(Tyr) (G psi A) and seven code for tRNA2(Tyr) (G psi A). The two tRNA species differ in one nucleotide pair at the basis of the T psi C stem. Only one tRNA(Tyr) gene (pNtY5) contains a point mutation (T54-->A54). Comparison of the intervening sequences reveals that they differ considerably in length and sequence. Maturation of intron-containing pre-tRNAs was studied in HeLa and wheat germ extracts. All pre-tRNAs(Tyr)--with one exception--are processed and spliced in both extracts. The tRNA(Tyr) gene encoded by pNtY5 is transcribed efficiently in HeLa extract but processing of the pre-tRNA is impaired.