DEVELOPMENTAL REGULATION OF PP44 46, TYROSINE-PHOSPHORYLATED PROTEINSASSOCIATED WITH TYROSINE/SERINE KINASE-ACTIVITY IN TRYPANOSOMA-BRUCEI/

The pattern of tyrosine-phosphorylated proteins is developmentally reg ulated in Trypanosoma brucei. To examine the function and regulation o f these tyrosine-phosphorylated molecules, monoclonal antibodies were generated using purified tyrosine-phosphorylated proteins as immunogen s. Two monoclonal antibodies were obtained. Both react with a set of p roteins at 44-46 kDa, collectively referred to as pp44/46, that are ph osphorylated on serine and tyrosine. Differentiation of the parasite f rom slender bloodforms to procyclic forms was accompanied by increased abundance and tyrosine-phosphorylation of pp44/46. The monoclonal ant ibodies immunoprecipitated protein kinase activity capable of phosphor ylating pp44/46 on serine and tyrosine, and myelin basic protein on se rine. The data indicate that the prominent tyrosine-phosphorylated pro teins induced upon differentiation are either themselves protein kinas es or that they are associated with protein kinases.