MOLECULAR ANALYSIS OF THE GAMMA-HEAVY CHAIN OF CHLAMYDOMONAS FLAGELLAR OUTER-ARM DYNEIN

We report here the complete sequence of the gamma dynein heavy chain o f the outer arm of the Chlamydomonas flagellum, and partial sequences for six other dynein heavy chains. The gamma dynein heavy chain sequen ce contains four P-loop motifs, one of which is the likely hydrolytic site based on its position relative to a previously mapped epitope. Co mparison with available cytoplasmic and flagellar dynein heavy chain s equences reveals regions that are highly conserved in all dynein heavy chains sequenced to date, regions that are conserved only among axone mal dynein heavy chains, and regions that are unique to individual dyn ein heavy chains. The presumed hydrolytic site is absolutely conserved among dyneins, two other P loops are highly conserved among cytoplasm ic dynein heavy chains but not in axonemal dynein heavy chains, and th e fourth P loop is invariant in axonemal dynein heavy chains but not i n cytoplasmic dynein. One region that is very highly conserved in all dynein heavy chains is similar to a portion of the ATP-sensitive micro tubule-binding domain of kinesin. Two other regions present in all dyn ein heavy chains are predicted to have high alpha-helical content and have a high probability of forming coiled-coil structures. Overall, th e central one-third of the gamma dynein heavy chain is most conserved whereas the N-terminal one-third is least conserved; the fact that the latter region is divergent between the cytoplasmic dynein heavy chain and two different axonemal dynein heavy chains suggests that it is in volved in chain-specific functions.