CHARACTERIZATION OF A POLO-LIKE PROTEIN-KINASE GENE HOMOLOG FROM AN EVOLUTIONARY DIVERGENT EUKARYOTE, TRYPANOSOMA-BRUCEI

The polo-like protein kinase gene family (PLKs) encodes proteins which are involved in the control of exit from mitosis in higher eukaryotes . We have cloned and analysed a polo-like kinase, tbplk, from an evolu tionary divergent eukaryote, Trypanosoma brucei. The gene encodes a 76 7 amino acid protein of predicted size 86.8 kDa with 50.4% identity to mammalian PLKs over the protein kinase catalytic domain and it posses ses a conserved motif, the 'polo-box', which is found in all PLKs. Phy logenetic analysis demonstrates that this gene is clearly a member of the PLK family, although it has some distinctive features such as a la rge C-terminal insertion when compared with mammalian PLKs. The gene i s single copy and expressed in both bloodstream and procyclic stage tr ypanosomes. Sequencing of tbplk from a number of trypanosome isolates reveals a length polymorphism in a run of asparagine residues within t he coding region. The presence of PLKs in a wide range of organisms, i ncluding such a primitive organism as T. brucei, suggests that PLKs ma y have a key role in the function of the cell cycle. (C) 1998 Elsevier Science B.V.