The FATTY ACID ELONGATION1 (FAE1) gene of Arabidopsis is required for the synthesis of very long chain fatty acids in the seed. The product of the FAE1 gene is presumed to be a condensing enzyme that extends the chain length of fatty acids from C18 to C20 and C22. We report here the cloning of FAE1 by directed transposon tagging with the maize element Activator (Ac). An unstable fae1 mutant was isolated in a line carrying Ac linked to the FAE1 locus on chromosome 4. Cosegregation and reversion analyses established that the new mutant was tagged by Ac. A DNA fragment flanking Ac was cloned by inverse polymerase chain reaction and used to isolate FAE1 genomic clones and a cDNA clone from a library made from immature siliques. The predicted amino acid sequence of the FAE1 protein shares homology with those of other condensing enzymes (chalcone synthase, stilbene synthases, and beta-ketoacyl-acyl carrier protein synthase III), supporting the notion that FAE1 is the structural gene for a synthase or condensing enzyme. FAE1 is expressed in developing seed, but not in leaves, as expected from the effect of the fae1 mutation on the fatty acid compositions of those tissues.
The late promoter of simian virus 40 (SV40) is activated in trans by the viral early gene product, T antigen. We inserted the wild-type late-promoter region, and deletion mutants of it, into chloramphenicol acetyltransferase transient expression vectors to identify promoter sequences which are active in the presence of T antigen. We defined two promoter activities. One activity was mediated by a promoter element within simian virus 40 nucleotides 200 to 270. The activity of this element was detectable only in the presence of an intact, functioning origin of replication and accounted for 25 to 35% of the wild-type late-promoter activity in the presence of T antigen. The other activity was mediated by an element located within a 33-base-pair sequence (simian virus nucleotides 168 to 200) which spans the junction of the 72-base-pair repeats. This element functioned in the absence of both the origin of replication and the T-antigen-binding sites and appeared to be responsible for trans-activated gene expression. When inserted into an essentially promoterless plasmid, the 33-base-pair element functioned in an orientation-dependent manner. Under wild-type conditions in the presence of T antigen, the activity of this element accounted for 65 to 75% of the late-promoter activity. The roles of the 33-base-pair element and T antigen in trans-activation are discussed.Transcription appears to be a key point for control of eucaryotic gene expression. Both the utilization of a transcriptional unit and the rate of its transcription can be controlled in response to environmental, metabolic, or developmental signals. Our present understanding of eucaryotic transcriptional control stems, in large part, from studies of the DNA viruses. One specific system, simian virus 40 (SV40), has repeatedly proven to be a useful model of both viral and cellular gene expression mechanisms. The circular, 5,243-base-pair (bp) SV40 genome is relatively simple, containing only two transcription units which are temporally expressed, early and late, during the lytic cycle (66). The early region is transcribed soon after final uncoating in the cell nucleus. The level of transcription from the early promoter is negatively autoregulated by the early gene product, T antigen (4, 34, 41, 51, 53, 61-63, 65). Conversely, late-region transcription is activated by T antigen (11,36,40), and late mRNA accumulates in large quantities in the later phases of the infection, after viral DNA replication (also activated by T antigen) has been initiated.The promoter for early transcription has been studied in detail. In common with many other RNA polymerase II promoters, it contains a Goldberg-Hogness TATA sequence which directs the site of transcription initiation (5,6,24,57). In addition, efficient transcription from the early promoter requires (i) specific binding of cellular factor(s) to guanine * cytosine-rich sequences within the 21-bp repeated region (see Fig. 1 ; 19, 20) and (ii) cis-activation by the 72-bp enhancer elements (22,23,31,43, 71). Any cellular fact...
A chimeric oat phytochrome structural gene with an uninterrupted coding region was constructed for expression of the monocot protein in transgenic plants. The structural gene was placed under the transcriptional control of either a light‐regulated oat phytochrome promoter or the constitutively active cauliflower mosaic virus 35S promoter. These genes were then introduced into Nicotiana tabacum and N.plumbaginifolia. None of the regenerated plants showed expression of oat phytochrome RNA when transcription was controlled by the oat promoter. In contrast, RNA was obtained in plants when the structural gene was functionally linked to the 35S promoter. Transformants expressing oat phytochrome RNA produced a full length 124‐kd polypeptide that was recognized by oat‐specific anti‐phytochrome monoclonal antibodies. The oat protein was a substrate for chromophore addition in tobacco as judged by its red/far‐red photoreversible sensitivity to trypsin degradation. Production of oat phytochrome in transgenic plants gave rise to increased phytochrome spectral activity in both light‐ and dark‐grown plants. This increased phytochrome content resulted in phenotypic changes in transformed plants, including semi‐dwarfism, darker green leaves, increased tillering and reduced apical dominance. The possible significance of expressing a biologically active phytochrome in transgenic plants is discussed.
The FATTYAClD ELONGATlONl (FAEl) gene of Arabidopsis is required for the synthesis of very long chain fatty acids in the seed. The product of the FAEl gene is presumed to be a condensing enzyme that extends the chain length of fatty acids from C18 to C20 and C22. We report here the cloning of FAE7 by directed transposon tagging with the maire element Activator (Ac). An unstable fael mutant was isolated in a line carrying Ac linked to the FAEl locus on chromosome 4. Cosegregation and reversion analyses established that the new mutant was tagged by Ac. A DNA fragment flanking Ac was cloned by inverse polymerase chain reaction and used to isolate FAEl genomic clones and a cDNA clone from a library made from immature siliques. The predicted amino acid sequence of the FAEl protein shares homology with those of other condensing enzymes (chalcone synthase, stilbene synthases, and p-ketoacyl-acyl carrier protein synthase lll), supporting the notion that FAE7 is the structural gene for a synthase or condensing enzyme. FAEl is expressed in developing seed, but not in leaves, as expected from the effect of the fael mutation on the fatty acid compositions of those tissues.
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