REGULATION OF MYOSIN REGULATORY LIGHT-CHAIN PHOSPHORYLATION VIA CYCLIC-GMP DURING CHEMOTAXIS OF DICTYOSTELIUM

Previous studies on the chemotactic movement of Dictyostelium have ind icated a role for cyclic GMP in regulating the association of myosin I I with the cytoskeleton. In this study we have examined the part playe d by phosphorylation of the 18 kDa myosin regulatory light chain in th is event. Using streamer F mutant NP368 (which is deficient in the str uctural gene for cyclic GMP-specific phosphodiesterase) we find that, for the regulatory light chain kinase, the major peak of phosphorylati on is delayed compared to the parental control strain XP55, occurring at 80 seconds rather than about 30 seconds in XP55. In two independent ly derived mutants that are unable to increase their cellular concentr ation of cyclic GMP (above basal levels) in response to a chemotactic stimulus of cyclic AMP (KI-10 and SA219), no increase in the phosphory lation of the light chain occurred, or movement of myosin II to the cy toskeleton. We also find a smaller peak of light chain phosphorylation that occurs within 10 seconds of cyclic AMP stimulation of the amoeba e, and which is absent in the cyclic GMP-unresponsive strains. We conc lude that cyclic GMP is involved in regulating light chain phosphoryla tion in this system. The possible significance of these findings is di scussed and a model that relates these findings to published data on c ytoskeletal myosin changes during chemotaxis is presented.