SEQUENCE, EXPRESSION AND LOCALIZATION OF CALMODULIN-DOMAIN PROTEIN-KINASES IN EIMERIA-TENELLA AND EIMERIA-MAXIMA

We have isolated and sequenced cDNA clones from Eimeria tenella and Ei meria maxima which encode proteins that share homology with a recently described family of calmodulin-domain protein kinases. The primary se quence data show that each of the protein kinases can be divided into 2 main functional domains-an amino-terminal catalytic domain typical o f serine/threonine protein kinases and a carboxy-terminal domain homol ogous to calmodulin, which is capable of binding calcium ions at 4 'EF -hand' motifs. Expression of the E. tenella calmodulin-domain protein kinase (EtCDPK) increased towards the end of oocyst sporulation, as ju dged by Northern and Western blotting, and indirect immunofluorescent antibody labelling showed that within a few minutes of adding sporozoi tes to target host cells in in vitro culture EtCDPK was found to be sp ecifically associated with a filament-like structure that converges at the apical end of the parasite. Once the parasite entered the host ce ll EtCDPK appeared to be left on the host cell membrane at the point o f entry, indicating a brief yet specific role for this molecule in the invasion of host cells by. E. tenella.