Involvement of tail domains in regulation of Dictyostelium myosin II

The actin-dependent ATPase activity of Dictyostelium myosin II filaments is regulated by phosphorylation of the regulatory light chain. Four deletion mutant myosins which lack different parts of subfragment 2 (S2) showed phos phorylation-independent elevations in their activities. Phosphorylation-ind ependent elevation in the activity was also achieved by a double point muta tion to replace conserved Glu932 and Glu933 in S2 with Lys. These results s uggested that inhibitory interactions involving the head and S2 are require d for efficient regulation. Regulation of wild-type myosin was not affected by copolymerization with a S2 deletion mutant myosin in the same filaments . Furthermore, the activity linearly correlated with the fraction of phosph orylated molecules in wild-type filaments. These latter two results suggest that the inhibitory head-tail interactions are primarily intramolecular, ( C) 2000 Academic Press.