Gene for Small Subunit for Ribulose Biophosphate Carboxylase rbcS, Regulated by phytochrome, Bisphosphate Carboxylase, Bisphosphate Oxygenase

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Study of Regulatory DNA Sequences Study of Regulatory DNA Sequences - Introduction Transgenes that are Inducible by a Stimulus or Exhibit Tissue Specific Expression In Transgenic Plants Regulatory Sequences of Induced Genes

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	Gene for small subunit of ribulose bisphosphate carboxylase (rbcS) Dozens of genes in plants are affected by light and many of these regulated by phytochrome. The expression of phytochrome gene is depressed and that of RUBISCO (ribulose, 1,5 bisphosphate carboxylase/oxygenase) gene is stimulated by red light. RUBISCO is involved in CO2 fixation and is the most abundant enzyme on the earth. It consists of two subunits, each encoded by a separate gene, the smaller subunit 'rbcS' encoded by a nuclear gene and the larger subunit 'rbcL' encoded by a chloroplast gene. Although, rbcS from different plants are fairly similar, small differences that exist, can be used to distinguish mRNA of a trans gene from that of the host plant using specific probes. For instance, pea rbcS gene was transferred to petunia and tobacco plants and the soybean rbcS gene was transferred to petunia.
The gene expressed itself in transgenic plants, rbcS subunit from the introduced gene sometimes even combining with rbcL subunit of the host plant to yield the enzyme. 'Deletion mutants' having sequences deleted upstream of the transgene rbcS led to the identification of a sequence upstream (-166 to -149 bp) of TATA box, which was light responsive and was therefore conveniently called 'light responsive element (LRE)'. This LRE sequence could also regulate genes other than rbcS genes so that these unrelated foreign genes became light, organ and age specific in a manner similar to rbcS gene (high expression in leaves, low expression in stem and no expression in roots).
LRE was shown to have three regions, box I, box II and box III and it was shown that box II region also had a negative regulatory element. This LRE also seems to be repetitive (with two repeats) and each repeat unit can mediate light responsiveness and organ specificity. However, it has also been shown that both repeats of LRE are required for full expression of the rbcS gene in youngest leaves of tobacco plants.It has also been shown using transgenic plants, that a different sequence upstream to rbcS is responsible for age responsiveness. For example, it was shown that the region from -41 to -166 bp is essential for high level of expression in mature leaves, but not important for light responsive expression in young leaves, for which the region -166 to -149 bp was most important.

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Gene for Small Subunit of Ribulose Biophosphate Carboxylase - rbcS Gene for Chlorophyll a/b Binding Protein - Cab Heat Shock Genes Alcohol Dehydrogenase Gene - ADH Genes for Seed Storage Proteins in Legumes and Cereals EPSP Synthase Gene

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