MULTIPLE SITES OF PHOSPHORYLATION WITHIN THE ALPHA-HEAVY-CHAIN OF CHLAMYDOMONAS OUTER ARM DYNEIN

We have examined the phosphorylation of the alpha dynein heavy chain ( DHC) from the outer arm of the Chlamydomonas flagellum. Quantitative a nalysis indicates that this DHC is phosphorylated at a minimum of six sites. Using previously identified proteolytic and photocleavage sites (King, S. M., and Witman, G. B. (1988) J. Biol. Chem. 263, 9944-9255) , we have mapped two regions that are phosphorylated in vivo. One is l ocated in a 20-kDa section immediately N-terminal to the site of V1 ph otocleavage. Thus, this region is close to the ATP hydrolytic site and also to the predicted junction between the head and stem domains of t he particle. The second encompasses the 90-kDa C-terminal region of th e molecule, In this latter section, at least one site is found in an s imilar to 2-kDa region close to domains that are predicted to adopt a coiled-coil structure in those DHCs that have been sequenced. The alph a DHC also is specifically labeled by endogenous kinases in demembrana ted, washed axonemes, suggesting that at least one alpha DHC kinase is located close to, or is a component of, the outer arm in situ.