Deletion of a novel protein kinase with PX and FYVE-related domains increases the rate of differentiation of Trypanosoma brucei

Growth control of African trypanosomes in the mammalian host is coupled to differentiation of a non-dividing life cycle stage, the stumpy bloodstream form. We show that a protein kinase with novel domain architecture is impor tant for growth regulation. Zinc finger kinase (ZFK) has a kinase domain re lated to RAC and S6 kinases flanked by a FYVE-related zinc finger and a pho x (PX) homology domain, To investigate the function of the kinase during cy clical development, a stable transformation procedure for bloodstream forms of differentiation-competent (pleomorphic) Trypanosoma brucei strains was established. Deletion of both allelic copies of ZFK by homologous recombina tion resulted in reduced growth of bloodstream-form parasites in culture, w hich was correlated with an increased rate of differentiation to the non-di viding stumpy form. Growth and differentiation rates were returned to wild- type level by ectopic ZFK expression. The phenotype is stage-specific, as g rowth of procyclic (insect form) trypanosomes was unaffected, and Delta zfk /Delta zfk clones were able to undergo full cyclical development in the tse tse fly vector. Deletion of ZFK in a differentiation defective (monomorphic ) strain of T. brucei did not change its growth rate in the bloodstream sta ge. This suggests a function of ZFK associated with the trypanosomes' decis ion between either cell cycle progression, as slender bloodstream form, or differentiation to the non-dividing stumpy form.