¹CRUK Clinical Centre at Leeds, Division of Cancer Medicine Research, St James's University Hospital, Leeds, UK

Correspondence: Dr E Morrison, Leeds Institute of Molecular Medicine, University of Leeds, St James's University Hospital, Beckett St, Leeds, W Yorks LS9 7TF, UK. E-mail: e.e.morrison@leeds.ac.uk

²Current address: Smith and Nephew Research Centre, York Science Park, York, UK.

Received 14 February 2007; Revised 14 September 2007; Accepted 20 September 2007; Published online 29 October 2007.

Abstract

The microtubule (MT)-associated protein EB1 localizes to and promotes growth at MT plus ends. The MT depolymerizing kinesin MCAK has also been reported to track growing MT plus ends. Here, we confirm that human MCAK colocalizes with EB1 at growing MT ends when expressed as a GFP fusion protein in transfected cells. We show that MCAK associates with the C-terminus of EB1 and EB3 but much less efficiently with RP1. EB1 associates with the N-terminal localization and regulatory domain in MCAK but not with the motor domain of the protein. The interaction is competitive with the binding of other EB1 ligands and does not require MTs. Knockdown of EB1 expression using siRNA impaired the ability of GFP-MCAK to localize to MT tips in transfected cells. We propose that MCAK is targeted to growing MT ends by EB1, that MCAK is held in an inactive conformation when associated with EB1 and that this could provide the basis for a mechanism that facilitates rapid switching between phases of MT growth and depolymerization.