The non-catalytic domain of the Xenopus laevis auroraA kinase localises the protein to the centrosome

Aurora kinases are involved in mitotic events that control chromosome segre gation. All members of this kinase subfamily possess two distinct domains, a highly conserved catalytic domain and an N-terminal non-catalytic extensi on that varies in size and sequence. To investigate the role of this variab le non-catalytic region we overexpressed and purified Xenopus laevis aurora A (pEg2) histidine-tagged N-terminal peptide from bacterial cells, The pept ide has no effect on the in vitro auroraA kinase activity, but it inhibits both bipolar spindle assembly and stability in Xenopus egg extracts, Unlike the full-length protein, the N-terminal domain shows only low affinity for paclitaxel-stabilised microtubules in vitro, but localises to the centroso mes in a microtubule-dependent manner. When expressed in Xenopus XL2 cells, it is able to target the green fluorescent protein to centrosomes, Surpris ingly, this is also true of the pEg2 catalytic domain, although to a lesser extent. The centrosome localisation of the N-terminal peptide was disrupte d by nocodazole whereas localisation of the catalytic domain was not, sugge sting that in order to efficiently localise to the centrosome, pEg2 kinase required the non-catalytic N-terminal domain and the presence of microtubul es.