CALMODULIN FUNCTION AND CALMODULIN-BINDING PROTEINS DURING AUTOACTIVATION AND SPORE GERMINATION IN DICTYOSTELIUM-DISCOIDEUM

Dictyostelium discoideum spores can be activated to initiate germinati on either endogenously via a diffusible autoactivator, or exogenously via heat. Following activation, three successive stages of germination occur, the lag stage, spore swelling and amoebal emergence. A previou s study [Lydan M. A. and Cotter D. A. (1994) FEBS Lett. 115, 137-142] has shown that spore swelling is dependent on the activity of calmodul in. In this study, the calmodulin antagonists trifluoperazine and calm idazolium inhibited autoactivation, but had no effect upon heat activa tion. These agents also inhibited amoebal emergence following either f orm of activation. The effects caused by the anti-calmodulin agents we re specific to an inhibition of calmodulin function since agents which modulate the activity of protein kinase C had no effect upon spore ge rmination. A calcium-dependent calmodulin-binding protein of about 64, 000 M(r) may be associated with the process of autoactivation since it was only seen in those spores which respond to the autoactivator. Ove rall, this study provides evidence to show that calmodulin plays a reg ulatory role during autoactivation and amoebal emergence during spore germination in D. discoideum and provides evidence for the calmodulin- dependent mechanisms which mediate each of these phases of germination .