RAMA1 is a novel kinetochore protein involved in kinetochore-microtubule attachment.
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.
Raaijmakers
Jonne A
JA
Department of Medical Oncology and Cancer Genomics Center, University Medical Center Utrecht, Utrecht, The Netherlands.
Tanenbaum
Marvin E
ME
Maia
André F
AF
Medema
René H
RH
D018797:Cell Cycle Proteins; D020090:Chromosome Segregation; D003598:Cytoskeletal Proteins; D006367:HeLa Cells; D006801:Humans; D018386:Kinetochores / Q000378:metabolism*; D008869:Microtubule-Associated Proteins / Q000235:genetics / Q000378:metabolism*; D008870:Microtubules / Q000378:metabolism*; D008938:Mitosis / Q000502:physiology*; D009687:Nuclear Proteins / Q000378:metabolism; D034622:RNA Interference; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D008941:Spindle Apparatus / Q000378:metabolism; D013997:Time Factors; D014162:Transfection
D018797:Cell Cycle Proteins; D003598:Cytoskeletal Proteins; D008869:Microtubule-Associated Proteins; C120529:NDC80 protein, human; D009687:Nuclear Proteins; D011993:Recombinant Fusion Proteins; C541140:Ska3 protein, human