Laboratory of Parasitology, Leiden University Medical Centre, The Netherlands.
The complete sequence of the cdc2-related kinase 2 (CRK2) gene from Plasmodium knowlesi and from P. berghei was determined. In both species, the CRK2 gene is closely linked to an elongation factor 1 alpha gene. The two CRK2 proteins are highly homologous to the P. falciparum PfPK5 protein. The CRK2 gene of both species is expressed at a low level during the asexual cell-cycle within the host erythrocytes. The P. berghei CRK2 mRNA is also present in gametocytes and in stages during development in the mosquito, suggesting a role of this protein in different parts of the life cycle. A conserved sequence located in the 5' untranslated region immediately upstream of the initiator ATG has the potential to form a stem-loop structure. Although the CRK2 protein possesses most of the domains that are conserved among cdc2-proteins, neither a recombinant P. knowlesi CRK2 protein nor a recombinant P. berghei protein was able to complement a yeast cdc28ts mutant. Furthermore and in contrast to the P. falciparum PfPK5 protein, a recombinant monomeric P. knowlesi CRK2 protein showed no kinase activity.