Published online
doi:10.1083/jcb.200610022
The Journal of Cell Biology, Vol. 176, No. 6, 819-829
The Rockefeller University Press, 0021-9525 $30.00
© Tam et al.
A CDK-related kinase regulates the length and assembly of flagella in Chlamydomonas
Lai-Wa Tam1,
Nedra F. Wilson1,2, and
Paul A. Lefebvre1
1 Department of Plant Biology, University of Minnesota, St. Paul, MN 55108
2 Department of Anatomy and Cell Biology, Oklahoma State University, Center for Health Sciences, Tulsa, OK 74107
Correspondence to Paul A. Lefebvre: pete{at}umn.edu
Little is known about how cells regulate the size of their organelles. In this study, we find that proper flagellar length control in Chlamydomonas reinhardtii requires the activity of a new member of the cyclin-dependent kinase (CDK) family, which is encoded by the LF2 (long flagella 2) gene. This novel CDK contains all of the important residues that are essential for kinase activity but lacks the cyclin-binding motif PSTAIRE. Analysis of genetic lesions in a series of lf2 mutant alleles and site-directed mutagenesis of LF2p reveals that improper flagellar length and defective flagellar assembly correlate with the extent of disruption of conserved kinase structures or residues by mutations. LF2p appears to interact with both LF1p and LF3p in the cytoplasm, as indicated by immunofluorescence localization, sucrose density gradients, cell fractionation, and yeast two-hybrid experiments. We propose that LF2p is the catalytic subunit of a regulatory kinase complex that controls flagellar length and flagellar assembly.
Abbreviations used in this paper: BAC, bacterial artificial chromosome; CDK, cyclin-dependent kinase; DIC, differential interference contrast; IFT, intraflagellar transport; LRC, length regulatory complex; PVDF, polyvinylidene difluoride; RACE, rapid amplification of cDNA ends; WT, wild type.

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