bop5 mutations reveal new roles for the IC138 phosphoprotein in the regulation of I1 dynein activity
Kristyn VanderWaal1, Ryosuke Yamamoto3, Raqual Bower1, Ritsu Kamiya3, Winfield S. Sale2, and Mary E. Porter1
1) GCD, University of Minnesota, Minneapolis, MN USA
2) Cell Biology, Emory University, Atlanta, GA USA
3) Biol. Sciences, University of Tokyo, Tokyo, Japan
Several lines of evidence indicate that the two-headed I1 inner arm dynein, also known as dynein f, plays a key role in the regulation of flagellar motility. Mutants lacking I1 dynein display altered waveforms and reduced phototaxis, but also partially suppress motility defects observed in central pair defective strains (Brokaw & Kamiya, 1987; King & Dutcher, 1994; Okita et al., 2005; Porter et al., 1992). Control of I1 dynein activity and microtubule sliding appears to be mediated through the radial spokes and phosphorylation of IC138 (Habermacher & Sale, 1997, Bower et al., 2009). Recent studies of bop5 mutations have revealed that IC138 is required for the assembly of a IC/LC subcomplex located at the base of the I1 dynein, between the 1st radial spoke and the outer dynein arms (Hendrickson et al., 2004, Ikeda et al., 2009; Bower et al., 2009). To understand how the IC138 phosphoprotein regulates I1 activity, we have now characterized the molecular lesions and motility phenotypes of several bop5 alleles in greater detail. Sequence analysis has shown that bop5-3, bop5-4, and bop5-5 are null alleles associated with deletions or premature stop codons, whereas bop5-6 is an intron mutation that alters IC138 expression. The motility phenotypes are similar to that of bop5-1, which encodes a truncated IC138 lacking the C-terminal WD repeat. The bop5 strains swim forwards with reduced swimming velocities, but phototaxis (as assayed by photoaccumulation) is relatively normal. However the reversal response associated with photoshock appears to be impaired. The motility defects are rescued by transformation with the wild-type IC138 gene. We are now analyzing flagellar waveforms to better understand the nature of the motility defects. Supported by NIH.
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