CHARACTERIZATION OF ADG1, AN ARABIDOPSIS LOCUS ENCODING FOR ADPG PYROPHOSPHORYLASE SMALL-SUBUNIT, DEMONSTRATES THAT THE PRESENCE OF THE SMALL-SUBUNIT IS REQUIRED FOR LARGE SUBUNIT STABILITY

Two mutants of Arabidopsis have been isolated that affect ADPG pyropho sphorylase (ADGase) activity. Previously, it has been shown that ADG2 encodes the large subunit of ADGase. This study characterizes the adg1 mutant phenotype and ADG1 gene structure. RNA blot analyses indicate that the adg1-1 mutant accumulates transcripts encoding both the large and small subunits of ADGase, while the adg1-2 mutant accumulates onl y large subunit transcripts. RFLP analysis and complementation of adg1 mutants with the ADGase small subunit gene demonstrate that ADG1 enco des the small subunit. Sequence analysis indicates that adg1-1 represe nts a missense mutation within the gene. Western blot analysis confirm s that adg1 mutants contain neither the large nor the small subunit pr oteins, suggesting that the presence of functional small subunits is r equired for large subunit stability.