Mutant/mutation
The mutant expresses a mutated form of CS in which the two putative pexel/VTS motifs are mutated. The conserved arginine and leucine were mutated to alanine by site directed mutagenesis. The endogenous cs gene was replaced with the mutated form.

Protein (function)
The CS protein is the major protein on the surface of sporozoites and is critical for development of sporozoites within the oocysts and is involved in motility and invasion of both the salivary gland of the mosquito and the liver cells. The protein is also found on the oocyst plasma membrane and on the inner surface of the oocyst capsule. Specific motifs in CS are involved in sporozoite binding to mosquito salivary glands and in sporozoite attachment to heparan sulfate proteoglycans in the liver of the mammalian host. During substrate-dependent locomotion of sporozoites, CS is secreted at the sporozoite anterior pole, translocated along the sporozoite axis and released on the substrate at the sporozoite posterior pole. Following sporozoite invasion of hepatocytes, the CS is released in the host cell cytoplasm.

Phenotype
The phenotype analyses indicate that mutation of the pexel/VTS motifs in the CS protein had no effect on the in vitro invasion of hepatocytes  by mutant sporozoites. However, development within hepatocytes was strongly reduced. Evidence is presented that expression of the mutated CS protein resulted in abortion of transport of CS into the cytoplasm of the host hepatocyte. The lack of CS release into the cytoplasm/nucleus of the hepatocyte affected the development of the liver stages.

Additional information
In wild type sporozoites, the CS-protein is cleaved at the N-terminal by a parasite cysteine protease, and this processing is required for infectivity. Although several substitutions were introduced in the amino terminus of the pexel/VTS of the CS mutants, the protein was processed correctly.

See also the mutant RMgm-614 which expresses the CS-protein with similar mutated Pexel/VTS motifs. For this mutant it was shown the CS was exported into the cytoplasm of the infected hepatocyte and no evidence was reported for affected CS export.

Other mutants
RMgm-285: Mutants expressing a CS-GFP fusion protein in blood stages. Mutants express the fusion protein in which the putative pexel/VTS motifs of the CS gene are mutated.