Mutant/mutation
The mutant lacks expression of two ookinete surface proteins, P25 and P28.

Protein (function)
P25 and P28 are two major surface proteins of the plasma membrane of ookinetes. The proteins are conserved between different Plasmodium species. The proteins are characterized by a secretory N-terminal signal sequence followed by three or four epidermal growth factor (EGF) domains and a glycosylphosphatidylinositol (GPI) anchor. Synthesis of both proteins begins between 0.5 and 2 h after the formation of the female gametes, and the proteins are still present in young oocysts. The paralogous genes encoding P25 and P28 are located next to each other in the genome in a head to tail organization.

Phenotype
In the midgut of mosquitoes, the formation of ookinetes lacking both proteins is significantly inhibited due to decreased protection against lethal factors, including protease attack. In addition, ookinetes have a much reduced capacity to traverse the midgut epithelium and to transform into the oocyst stage.

Additional information
In this mutant the genes encoding P25 and P28 have been disrupted (double knock-out mutant) using a single DNA construct.
Disruption of either p25 or p28 ('single knock-out' mutants) has only a minor effect on ookinete and oocyst production, indicating redundancy in function between P25 and P28.
Motility and entry into insect cells in vitro of the mutant ookinetes are normal, but the number of ookinetes successfully transforming into oocysts in vitro is significantly reduced (Sidén-Kiamos et al., J. Cell Science (2000) 113, 3419-26).

Other mutants
A. P. berghei mutant has been generated lacking P28 (RMgm-1).
A. P. berghei mutant has been generated lacking P25 (RMgm-2).