page 47, Rupp and Porter provide the first molecular characterization of a component of the dynein regulatory complex (DRC), a crucial but poorly understood regulator of flagellar movement. Besides suggesting a model for DRC assembly, the work identifies a possible connection between motility regulation and a theoretical mechanism of cell growth arrest.
Using insertional mutagenesis in Chlamydomonas, the authors identified a new mutation in the PF2 locus that causes motility defects. Further analysis showed that PF2 encodes subunit 4 of the DRC. The PF2 protein is uniformly distributed along the length of the axoneme and also associates with the basal body region, and its predicted structure has several coiled-coil domains that could mediate protein–protein interactions. PF2 mutants fail to assemble five of the seven known DRC subunits.
The results suggest that PF2 acts as a molecular scaffold, stabilizing the DRC by interacting with other components of the complex. Close homologues of PF2 occur in a wide range of cell types, and include a trypanosome gene product required for directional motility, and mouse and human gene products enriched in growth-arrested cells. One exciting possibility is that primary cilia containing PF2 homologues may transmit a signal to the cell to initiate growth arrest. As a first step in confirming this idea, the localization of PF2-related products must be determined in cells lacking flagella. ▪