<i>Chlamydomonas</i> IC97, an intermediate chain of the flagellar dynein f/I1, is required for normal flagellar and cellular motility

IDA f/I1 is a hetero-dimeric flagellar dynein that is particularly important for the regulation of flagellar waveform and whose defects are associated with human ciliopathies. IC97 is an evolutionarily conserved intermediate chain of IDA f/I1, but the detailed molecular functions of IC97 in flagellar motility have not been elucidated. In this study, mutational and biochemical analyses of the previously uncharacterized <i>Chlamydomonas ic97</i> mutant revealed that IC97 is required for both the normal flagellar and cellular motility. In particular, IC97 appears to play an important role in both the control of flagellar beat frequency and the coordination between the two (<i>cis</i>- and <i>trans</i>-) flagella in <i>Chlamydomonas</i>. Our results provide important insights into the regulation of IDA-f/I1 activity by IC97 and the pathogenetic mechanisms of human ciliopathies caused by IDA-f/I1 defects.