Radial spokes of Chlamydomonas flagella: genetic analysis of assembly and function.

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Abstract
The previously studied pf-14 and pf-1 loci in C. reinhardtii and mutations for another 5 genes (pf-17, pf-24, pf-25, pf-26 and pf-27) were identified and characterized as specifically affecting the assembly and function of the flagellar radial spokes. Mutants for each newly identified locus showed selective alterations for 1 or more of the 17 polypeptides in the MW range of 20,000-130,000 which formed the radial spoke structure. In specific instances the molecular defect was correlated with altered radial spoke morphology. Biochemical analysis of in vivo complementation in mutant X wild-type dikaryons provided indirect evidence that mutations for 4 of the 5 new loci (pf-17, pf-24, pf-25 and pf-26) reside in structural genes for spoke components. In the case of pf-24, the identity of the mutant gene product was supported by analysis of induced intragenic revertants. Evidently the gene product in pf-27 was extrinsic to the radial spokes and may be required for the specific in vivo phosphorylation of spoke polypeptides.