Gene Enzyme and Physiological Characterization of shrunken-2Isoalleles

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9316887 Hannah The allosteric properties of ADP-glucose pyrophosphorylase are critical in controlling the amount of glucose polymers in organisms ranging from E. coli to potato. The maize transposable element, dissociation Ds, was placed within the coding region of the site of a gene encoding the maize endosperm enzyme. Ds excisions are imprecise, thus revertants represent a series of closely-related mutations arising from one position in the gene. This form of in- vivo, site-specific mutagenesis was used to create wild type variants that differ in DNA sequence, enzyme levels, allosteric properties and seed weight. Since starch comprises 70% of seed weight, starch content likely has been altered. This research will further characterize revertants at DNA, enzyme and physiological levels. Additional excision events will identify changes at this site not only restoring gene function, but those not restoring gene function. Integration of studies at the gene, enzyme and physiological levels of the isogenic maize lines will help define the structure/function relationships of a important region of a critical enzyme and how these changes affect starch content. Secondly, these studies are providing new insight into the mechanism of Ds transposition. Unexpectedly some revertants do not easily fit current models of transposition. Additional excision events should lead to modification of existing models or to development of new ones. In summary, a series of integrated experiments are proposed to more clearly understand how this region of the enzyme affects its allosteric properties and, in turn, how changes affect starch biosynthesis. Coupled with this will be a better understanding of how Ds acts as a mutagen. ***