A Novel Ankyrin-Repeat Protein Interacts with the Regulatory Proteins of Inner Arm Dynein f (I1) of Chlamydomonas reinhardtii

How ciliary and flagellar motility is regulated is a challenging problem. The flagellar movement in Chlamydomonas reinhardtii is in part regulated by phosphorylation of a 138 kD intermediate chain (IC138) of inner arm dynein f (also called I1). In the present study, we found that the axoneme of mutants lacking dynein f lacks a novel protein having ankyrin repeat motifs, registered as FAP120 in the flagellar proteome database. FAP 120 is also missing or decreased in the axonemes of bop5, a mutant that has a mutation in the structural gene of IC138 but assembles the dynein f complex. Intriguingly, the amounts of FAP120 in the axonemes of different alleles of bop5 and several dynein f-lacking mutants roughly parallel their contents of IC138. These results Suggest a weak but stoichiometric interaction between FAP120 and IC138. We propose that FAP120 functions in the regulatory process as part of a protein complex involving IC138. Cell Motil. Cytoskeleton 66: 448-456, 2009. (C) 2008 Wiley-Liss. Inc.