Abstract
In Chlamydomonas , the central pair (CP) and radial spoke (RS) complexes in the axoneme are key regulators of ciliary motility. Radial spoke protein 3 (RSP3) is an A-kinase anchoring protein (AKAP), and mutation of the RII-binding domain ( 388 ) results in specific ciliary motility defects. When combined with ida1 , a mutant defective in the 1α-dynein heavy chain required for assembly of the I1 dynein complex, the phenotype of the resulting 388; ida1 double mutant is ida1 -like, not 388 -like; thus, ida1 is epistatic to 388 . These results support I1 dynein being downstream of the RSP3 RII-binding domain function in a signaling pathway that regulates Chlamydomonas ciliary motility.