This research seeks to determine the mechanisms by which the plant chromoprotein, phytochrome, photoreversibly regulates the activity of nuclear enzymes, especially that of a chromatin-associated nucleoside triphosphatase (NTPase). The research is designed to follow up and extend earlier findings which showed that red-light activated phytochrome could stimulate NTPase activity and nuclear protein phosphorylation in isolated pea nuclei and that Ca2+ and calmodulin played important roles in this response. It will be determined how much Ca2+ is required to support the NTPase stimulation and determine whether red light induces a change in the free ?Ca2+! in the nuclear preparation. Phytochrome will be immunocytochemically localized in isolated nuclei to help evaluate where within the preparation it may be functioning. Binding of purified NTPase to DNA will be studied. Specific DNA sequences that are recognized by the enzyme will be sought. There is evidence the NTPase may be phosphorylated by a spermine-activated NII kinase. This kinase will be isolated and characterized to test whether it can phosphorylate the NTPase and whether its activation is promoted also by calcium.%%% Results expected from the proposed experiments should contribute significantly to an improved understanding of how light and Ca2+ can regulate nuclear metabolism, with possible implications also for models of how phytochrome regulates gene expression. The ultimate aim of this project is to understand how the plant photoreceptor, phytochrome, controls growth and development changes in plants. Current data favor the hypothesis that phytochrome achieves this control in many instances by inducing specific alterations of membrane properties in target cells.***//
