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Vol. 20, Issue 13, 3055-3063, July 1, 2009

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IC138 Defines a Subdomain at the Base of the I1 Dynein That Regulates Microtubule Sliding and Flagellar Motility

Raqual Bower^*, Kristyn VanderWaal^*, Eileen O'Toole, Laura Fox, Catherine Perrone^*, Joshua Mueller^*, Maureen Wirschell, R. Kamiya, Winfield S. Sale, and Mary E. Porter^*

*Department of Genetics, Cell Biology, and Development, University of Minnesota, Minneapolis, MN 55455; Laboratory for 3D Fine Structure, Molecular, Cellular, and Developmental Biology, University of Colorado, Boulder, CO 80309; Department of Cell Biology, Emory University School of Medicine, Atlanta, GA 30322; and Department of Biological Sciences, Graduate School of Science, University of Tokyo, Tokyo 113-0033, Japan

Submitted April 8, 2009; Accepted April 29, 2009
Monitoring Editor: Erika Holzbaur

To understand the mechanisms that regulate the assembly and activity of flagellar dyneins, we focused on the I1 inner arm dynein (dynein f) and a null allele, bop5-2, defective in the gene encoding the IC138 phosphoprotein subunit. I1 dynein assembles in bop5-2 axonemes but lacks at least four subunits: IC138, IC97, LC7b, and flagellar-associated protein (FAP) 120—defining a new I1 subcomplex. Electron microscopy and image averaging revealed a defect at the base of the I1 dynein, in between radial spoke 1 and the outer dynein arms. Microtubule sliding velocities also are reduced. Transformation with wild-type IC138 restores assembly of the IC138 subcomplex and rescues microtubule sliding. These observations suggest that the IC138 subcomplex is required to coordinate I1 motor activity. To further test this hypothesis, we analyzed microtubule sliding in radial spoke and double mutant strains. The results reveal an essential role for the IC138 subcomplex in the regulation of I1 activity by the radial spoke/phosphorylation pathway.

Address correspondence to: Mary E. Porter (porte001{at}umn.edu)

Abbreviations used: DRC, dynein regulatory complex; FAP, flagellar-associated protein; HC, heavy chain; IC, intermediate chain; LC, light chain; MBO, move backwards only; PKI, protein kinase inhibitor; TAP, Tris acetate phosphate.

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