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First published online 23 June 2009
doi: 10.1242/jcs.051912

Journal of Cell Science 122, 2436-2445 (2009)
Published by The Company of Biologists 2009
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Research Article

RAMA1 is a novel kinetochore protein involved in kinetochore-microtubule attachment

Jonne A. Raaijmakers*, Marvin E. Tanenbaum*, André F. Maia and René H. Medema{ddagger}

Department of Medical Oncology and Cancer Genomics Center, University Medical Center Utrecht, Utrecht, The Netherlands

{ddagger} Author for correspondence (e-mail: r.h.medema{at}umcutrecht.nl)

Accepted 28 April 2009

During mitosis, kinetochores need to attach to microtubules emanating from spindle poles. Several protein complexes have been shown to mediate the kinetochore-microtubule interaction. However, with the continually growing number of newly identified kinetochore proteins, it is unclear whether all major components of the kinetochore-microtubule interface have been identified. We therefore performed a high-throughput RNAi screen to identify additional factors involved in kinetochore-microtubule attachment, and identified RAMA1 as a novel regulator of this process. Depletion of RAMA1 results in severe chromosome alignment defects and a checkpoint-dependent mitotic arrest. We show that this is due to reduced kinetochore-microtubule attachments. RAMA1 localizes to the spindle and to outer kinetochores throughout all phases of mitosis and is recruited to kinetochores by the core kinetochore-microtubule attachment factor Hec1. Interestingly, unlike Hec1, the association of RAMA1 with kinetochores is highly dynamic, suggesting that it is not a structural component of the kinetochore. Consistent with this, all other kinetochore proteins tested do not require RAMA1 for their kinetochore localization. Taken together, these results identify RAMA1 as a novel kinetochore protein and suggest that RAMA1 may have a direct role in mediating kinetochore-microtubule interactions.

Key words: C13orf3, Kinetochore, Microtubule, Spindle


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