SEQUENCE-ANALYSIS OF THE CHLAMYDOMONAS ALPHA-DYNEIN AND BETA-DYNEIN HEAVY-CHAIN GENES

We have sequenced genomic clones spanning the complete coding region o f one heavy chain (beta) and the catalytic domain of a second (alpha) of the Chlamydomonas rein-hardtii flagellar outer arm dynein ATPase. T he beta heavy chain gene (ODA-4 locus) spans 20 kb, is divided into at least 30 exons, and encodes a predicted 520 kDa protein. Comparison w ith sea urchin beta dynein sequences reveals homology that extends thr oughout both proteins. Over the most conserved central catalytic regio n, the Chlamydomonas alpha and beta chains are equally divergent from the sea urchin beta chain (64% and 65% similarity, respectively), wher eas the Chlamydomonas gamma chain is more divergent from urchin beta ( 54% similarity). The four glycine-rich loops identified as potential n ucleotide-binding sites in other dynein heavy chains are also present in Chlamydomonas alpha and beta dyneins. Two of these four nucleotide- binding motifs are highly conserved among flagellar dyneins, but only the motif previously identified as the catalytic site in sea urchin dy nein is highly conserved between flagellar and cytoplasmic dynein heav y chains. Predictions of secondary structure suggest that all dynein h eavy chains possess three large domains, with the four nucleotide-bind ing consensus sequences located in a central 185 kDa domain that is bo unded on both sides by regions that form multiple, short alpha-helical coiled-coils.