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Dynactin drives dynein without microtubule binding

Organelle cargo distribution is similar in wild-type cells (left) and cells expressing nonmicrotubule-binding dynactin (right), indicating that transport remains intact.

Dynactin might bind to and organize microtubules. But it doesn't need to bind microtubules to jump-start dynein motoring, Kim et al. report on page 641.

Dynactin retrieves microtubule motors such as dynein from the cytoplasm and docks them onto their cargo. Dynactin also anchors the minus ends of microtubules on the centrosome.

One dynactin isoform that is found in human neurons lacks its microtubule-binding domain (MBD). Kim and colleagues thus supposed that dynactin might be functional even without locking onto microtubules. They found that indeed cargo transport does not rely on the MBD.

With or without a functional MBD, dynactin helped move four different physiological cargos, including vesicles and proteins, just as far along microtubules and at the same velocity and frequency.

Dynactin's MBD was previously thought to increase dynein's processivity by giving it a second hand to hang onto microtubules. But this idea was based largely on studies of the transport of dynein-coated beads. This artificial cargo, or the way dynein and dynactin were attached to it, might have altered the normal relations between dynein and dynactin observed in a cell.

Not all dynactin activities were unaffected by the loss of the MBD, however. Cells expressing the MBD-deleted form commonly arrested in prometaphase with multipolar spindles, suggesting a failure of microtubules to correctly conjoin in centrosomes and thus a role of dynactin in latching together microtubules.

Ruth Williams

ruth.williams{at}rockefeller.edu

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Microtubule binding by dynactin is required for microtubule organization but not cargo transport

Hwajin Kim, Shuo-Chien Ling, Gregory C. Rogers, Comert Kural, Paul R. Selvin, Stephen L. Rogers, and Vladimir I. Gelfand
J. Cell Biol. 2007 176: 641-651. [Abstract] [Full Text] [PDF]

This Article Full Text (PDF, 898K) PPT slides of all figures Alert me when this article is cited Services Email this article Similar articles in this journal Alert me to new content in the JCB Download to citation manager Citing Articles Citing Articles via CrossRef Citing Articles via Google Scholar Google Scholar Articles by Williams, R. Search for Related Content PubMed Articles by Williams, R. Related Collections Related Article Social Bookmarking                            What's this?