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J. Cell Biol.,
Volume 144, Number 3, February 8, 1999 473-481
Department of Cell Biology, University of Massachusetts Medical School, Worcester, Massachusetts 01655
Dyneins are microtubule-based molecular
motors involved in many different types of cell movement. Most dynein heavy chains (DHCs) clearly group
into cytoplasmic or axonemal isoforms. However, DHC1b has been enigmatic. To learn more about this
isoform, we isolated Chlamydomonas cDNA clones encoding a portion of DHC1b, and used these clones to
identify a Chlamydomonas cell line with a deletion mutation in DHC1b. The mutant grows normally and appears to have a normal Golgi apparatus, but has very
short flagella. The deletion also results in a massive redistribution of raft subunits from a peri-basal body pool
(Cole, D.G., D.R. Diener, A.L. Himelblau, P.L. Beech,
J.C. Fuster, and J.L. Rosenbaum. 1998. J. Cell Biol.
141:993-1008) to the flagella. Rafts are particles that
normally move up and down the flagella in a process
known as intraflagellar transport (IFT) (Kozminski,
K.G., K.A. Johnson, P. Forscher, and J.L. Rosenbaum.
1993. Proc. Natl. Acad. Sci. USA. 90:5519-5523), which
is essential for assembly and maintenance of flagella.
The redistribution of raft subunits apparently occurs due to a defect in the retrograde component of IFT,
suggesting that DHC1b is the motor for retrograde IFT.
Consistent with this, Western blots indicate that
DHC1b is present in the flagellum, predominantly in
the detergent- and ATP-soluble fractions. These results
indicate that DHC1b is a cytoplasmic dynein essential for flagellar assembly, probably because it is the motor
for retrograde IFT.
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