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 analysis 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, 9244-9255), we have mapped two regions that are phosphorylated in vivo. One is located in a 20-kDa section immediately N-terminal to the site of V1 photocleavage. Thus, this region is close to the ATP hydrolytic site and also to the predicted junction between the head and stem domains of the particle. The second encompasses the 90-kDa C-terminal region of the molecule. In this latter section, at least one site is found in an approximately 2-kDa region close to domains that are predicted to adopt a coiled-coil structure in those DHCs that have been sequenced. The alpha DHC also is specifically labeled by endogenous kinases in demembranated, washed axonemes, suggesting that at least one alpha DHC kinase is located close to, or is a component of, the outer arm in situ.