Fig. 1. Classification of Bub1-like proteins in Drosophila. Protein sequence analyses were done using Clustal X (http://www-igbmc.u-strasbg.fr/BioInfo/ClustalX/). Dm, Drosophila melanogaster; Hs, Homo sapiens; m, Mus musculus; X, Xenopus laevis; Sc, Saccharomyces cerevisiae; Sp, Saccharomyces pombe; An, Anopheles gambiae; Ce, Caenorhabditis elegans. (A) Sequence alignment of the KEN box motif uniquely present in the N-termini of BubR1 and Mad3 proteins. Note that DmBub1 (165 kDa) previously reported as Bub1 contains the KEN box motif similarly to other BubR1 proteins. (B) Sequence alignment of the C-terminal Ser/Thr kinase domains of Bub1 and BubR1 proteins. The 12 subdomains conserved among protein kinases (Hanks and Hunter, 1995) are underlined and the amino acids conserved within these subdomains are in red. In comparison with BubR1 kinases from other organisms, Drosophila BubR1 (DmBub1-165kDa) contains a much more conserved kinase domain. (C) Schematic representations of the Mad3, Bub1 and BubR1 proteins showing the relative positions of the KEN box motif present in Mad3 and BubR1 (crossed hatched box), the conserved Cdc20- and Bub3-binding domains present in all of them (black and grey boxes, respectively), and the conserved Ser/Thr kinase domain in Bub1 and BubR1 (vertical hatched box). Species that contain Mad3 and Bub1 or Bub1 and BubR1 are indicated on the right. (D) Phylogeny of the complete sequences of Bub1 and Mad3/BubR1 proteins.