PHYLOGENY AND EXPRESSION OF AXONEMAL AND CYTOPLASMIC DYNEIN GENES IN SEA-URCHINS

Transcripts similar to 14.5 kilobases in length from 14 different gene s that encode for dynein heavy chains have been identified in poly(A) RNA from sea urchin embryos. Analysis of the changes in level of thes e dynein transcripts in response to deciliation, together with their s equence relatedness, suggests that 11 or more of these genes encode dy nein isoforms that participate in regeneration of external cilia on th e embryo, whereas the single gene whose deduced sequence closely resem bles that of cytoplasmic dynein in other organisms appears not to be i nvolved in this regeneration. The four consensus motifs for phosphate binding found previously in the beta heavy chain of sea urchin dynein are present in all five additional isoforms for which extended sequenc es have been obtained, suggesting that these sites play a significant role in dynein function. Sequence analysis of a similar to 400 amino a cid region encompassing the putative hydrolytic ATP-binding site shows that the dynein genes fall into at least six distinct classes. Most o f these classes in sea urchin have a high degree of sequence identity with one of the dynein heavy chain genes identified in Drosophila, ind icating that the radiation of the dynein gene family into the present classes occurred at an early stage in the evolution of eukaryotes. Evo lutionary changes in cytoplasmic dynein have been more constrained tha n those in the axonemal dyneins.