Structure and organization of genes for sporozoite surface antigens

The major surface antigen (circumsporozoite-protein) of the sporozoite stage of Plasmodium knowlesi has been cloned and characterized. The gene is notable for the presence of a 36 base pair unit repeated in tandem 12 times. These repeats may function at the DNA level in regulating gene expression and at the protein level in providing multiple copies of a single epitope (repitope) as part of a protein designed to evade and decoy the immune system.