The Xenopus laevis centrosome aurora/lpl1-related kinase

The cDNA encoding the protein kinase pEg2 was originally cloned through a d ifferential screening performed during the early development of Xenopus lae vis. pEg2 orthologues were found in various organisms and were classified i n a new family of oncogenic mitotic protein kinases named 'aurora/Ipl1-rela ted kinases' after the Drosophila melanogaster gene aurora and the Saccharo myces cerevisiae gene Ipl1. The catalytic activity of pEg2 is necessary for the mitotic microtubule spindle formation in Xenopus laevis egg extracts. The addition of a dominant negative form of pEg2 to in vitro spindle assemb ly assays leads to monopolar spindles generated by a defect of centrosome s eparation. In Xenopus cultured cells, pEg2 was confined around the pericent riolar material once centrosomes were duplicated. The centrosome localizati on does not depend on the presence of microtubules. However, in vitro, the protein binds to taxol-stabilized microtubules independently of its kinase activity. During mitosis the location of the protein changes, in metaphase the kinase localizes on the microtubules at the poles of the mitotic spindl e whereas it is not present on astral microtubules. This localization persi sts until the segregation of the chromosomes is completed. The presence of the kinase on the spindle may reveal another yet unknown function. (C) 1999 Editions scientifiques et medicales Elsevier SAS.