Differential accumulation of a protein kinase homolog in Trypanosoma brucei

Using degenerate oligonucleotide primers derived from conserved regions in the catalytic domains of protein kinases, we have identified transcripts of the protein kinase families in Trypanosoma brucei by the polymerase chain reaction technique. From the cDNAs synthesized from poly(A)+ RNA purified from the bloodstream form of the pathogen, we have obtained seven distinct partial cDNA sequences. Deduced amino acid sequences of these seven clones contain conserved regions characteristic of catalytic domains of eukaryotic protein serine/threonine kinases. DNA gel blots showed that one of the clones, TbPK-A4 is most likely a member of a subfamily in the protein kinase gene family, whereas the other six are probably each encoded by a single gene in the genome of T. brucei. The full-length cDNA of TbPK-A1 was cloned, sequenced, and found to encode an open reading frame of 350 amino acid residues. Its gene (designated KFR1) demonstrated high sequence similarity to KSS1 and FUS3 from Saccharomyces cerevisiae and rat MAP kinase at the amino acid level. There are a 3- to 4-fold higher level of KFR1 transcript and a 2-fold increase of KFR1 protein in the bloodstream form when compared with the insect form of T. brucei. This preferential expression of KFR1 in the bloodstream form of T. brucei may play a role in controlling the cell cycle and thus the growth rate of the organism.