ADP-glucose pyrophosphorylase (ATP: alpha-glucose-I-phosphate adenylyl transferase, ADGase) previously has been studied as a key regulatory enzyme in the starch biosynthetic pathway in plant. Surprisingly, ADP-glucose pyrophosphorylase small subunit APSI (ADGl) was found not only in chloroplast but also in non plastidic region, especially, small proportion in nucleus. To elucidate the novel mechanislDS underlying non plastidic ADGI actions, yeast two-hybrid screening was used to identify proteins associated with ADGl. Yeast two hybrid and co-immunoprecipitation (Co-IP) assay were used to confirm the interaction between ADGl and interacting candidates. Furthermore, localization of interacting proteins was analyzed using Green Fluorescent Protein (GFP) fusion proteins under laser scanning microscopy. Two protein RPC4 (RNA polymerase III subunit) and LSU3 (Response to low Sulfur 3) were confirmed as strong candidates that interact with ADGl. Therefore, the authors hypothesized that non plastidic localized ADGl might have additional function which mediates plant cellular metabolism status and intracellular signaling to regulate proper plant growth and development.