A split motor domain in a cytoplasmic dynein

The heavy chain of dynein forms a globular motor domain that tightly couple s the ATP-cleavage region and the microtubule-binding site to transform che mical energy into motion along the cytoskeleton. Here we show that, in the fungus Ustilago maydis, two genes, dyn1 and dyn2, encode the dynein heavy c hain. The putative ATPase region is provided by dyn], while dyn2 includes t he predicted microtubule-binding site. Both genes are located on different chromosomes, are transcribed into independent mRNAs and are translated into separate polypeptides. Both Dyn1 and Dyn2 co-immunoprecipitated and co-loc alized within growing cells, and Dyn1-Dyn2 fusion proteins partially rescue d mutant phenotypes, suggesting that both polypeptides interact to form a c omplex. In cell extracts the Dyn1-Dyn2 complex dissociated, and microtubule affinity purification indicated that Dyn1 or associated polypeptides bind microtubules independently of Dyn2. Both Dyn1 and Dyn2 were essential for c ell survival, and conditional mutants revealed a common role in nuclear mig ration, cell morphogenesis and microtubule organization, indicating that th e Dyn1-Dyn2 complex serves multiple cellular functions.