Protein kinases in divergent eukaryotes: identification of protein kinase activities regulated during trypanosome development.

The role of protein kinases in organisms that diverged early in the eukaryotic lineage is relatively unexplored. In this study, we determined that primitive parasitic protozoa possess multiple protein-serine kinases and inferred the presence of protein-tyrosine kinases through sensitive immunoblotting techniques. To further explore the role of protein kinases in parasite development, we examined the activity of eight renaturable protein kinases during the life cycle of the protozoan parasite Trypanosoma brucei. The activities of six protein-serine/threonine kinases were regulated during development, with several distinct patterns of regulation. In addition, an 89-kDa protein kinase was detected in dividing cells but not in nondividing cells. Our data indicate that even the most primitive eukaryotes possess a large complement of protein kinases, including protein-tyrosine kinases as well as protein-serine/threonine kinases. The data further suggest that protein kinases may play a pivotal role in regulation of proliferation and differentiation in protozoa.