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Vol. 19, Issue 7, 3097-3110, July 2008

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Regulation of Microtubule Assembly and Organization in Mitosis by the AAA+ ATPase Pontin

Daniel Ducat^*,, Shin-ichi Kawaguchi^*,, Hongbin Liu^,||, John R. Yates, III, and Yixian Zheng^*,

*Department of Embryology, Carnegie Institution for Science and Howard Hughes Medical Institute, Baltimore, MD 21210; Department of Biology, Johns Hopkins University, Baltimore, MD 21218; and Department of Cell Biology, The Scripps Research Institute, La Jolla, CA 92037

Submitted December 1, 2007; Revised April 21, 2008; Accepted April 30, 2008
Monitoring Editor: Stephen Doxsey

To identify novel proteins important for microtubule assembly in mitosis, we have used a centrosome-based complementation assay to enrich for proteins with mitotic functions. An RNA interference (RNAi)-based screen of these proteins allowed us to uncover 13 novel mitotic regulators. We carried out in-depth analyses of one of these proteins, Pontin, which is known to have several functions in interphase, including chromatin remodeling, DNA repair, and transcription. We show that reduction of Pontin by RNAi resulted in defects in spindle assembly in Drosophila S2 cells and in several mammalian tissue culture cell lines. Further characterization of Pontin in Xenopus egg extracts demonstrates that Pontin interacts with the gamma tubulin ring complex (-TuRC). Because depletion of Pontin leads to defects in the assembly and organization of microtubule arrays in egg extracts, our studies suggest that Pontin has a mitosis-specific function in regulating microtubule assembly.

Present addresses: Temasek Life Sciences Laboratory, Singapore 117604, Singapore;

^|| Protein Analytical Chemistry, Genentech, South San Francisco, CA 94080.

Address correspondence to: Daniel Ducat (ducat{at}ciwemb.edu) or Yixian Zheng (zheng{at}ciwemb.edu)