The 78, 000-Mr intermediate chain of Chlamydomonas outer arm dynein is a microtubule binding protein

Abstract

Chem. 266:8401-8407) showed that the 78,000-Mr intermediate chain (IC78) from the Chlamydomonas outer arm dynein is in direct contact with e~-tubulin in situ, suggesting that this protein may be involved in binding the dynein to the doublet microtubules. Molecular genetic analysis of this chain recently demonstrated that it is a WD repeat protein essential for outer arm assembly (Wilkerson et al., 1995. J. Cell Biol. 129:169-178). We have now transcribed and translated IC78 in vitro, and demonstrate that this molecule binds axonemes and microtubules, whereas a homologous protein (the 69,000-M r intermediate chain [IC69] of Chlamydomonas outer arm dynein) does not. Thus, IC78 is a bona fide microtubule-binding protein. Taken together with the previous results, these findings indicate that IC78 is likely t