Mutant/mutation
The mutant lacks expression of SAP1 (sporozoite asparagine-rich protein; S22; SLARP, sporozoite and liver stage asparagine-rich protein).

Protein (function)
SAP1 was first identified as a sporozoite-expressed gene in a suppression subtractive hybridization (SSH) screen of P.  yoelii salivary gland sporozoites versus blood-stage merozoites (designated S22, sporozoite-specific gene 22).

Phenotype
The phenotype analyses indicate an essential role during the transformation of the sporozoite into the liver trophozoite within the hepatocyte and mutant parasites show a complete attenuation of liver stage development.  Mutant salivary gland sporozoites showed strongly reduced transcript abundance for several genes encoding proteins that play a role in infection of the liver, UIS3, UIS4 and P52 but not SPECTs, TRAP and CSP, indicating a selective mechanism of UIS transcript depletion. Based on these observations and its cytoplasmic location it has been suggested that SAP1 plays a role in translational repression of transcripts in sporozoites. See also 'Additional Information'  for a possible different function of SAP1 and additional analyses of the phenotype of this mutant described by Aly, A.S et al. (2011; Mol. Microbiol. 79, 929-39).

Additional information
No parasitophorous vacuole membrane (PVM) could be detected using antibodies against UIS4. Electron microscope analysis showed the presence of the PVM in a number of parasites.
Immunization of mice with the attenuated sporozoites of the mutant parasites induced protective immune responses against challenge with wild type parasites. See also RMgm-185, a P. berghei mutant lacking expression of SAP1/SLARP. Immunization with  sporozoites of this P. berghei  mutant confers only limited protective immunity.

By IFA analysis using antibodies against SAP1 a specific sporozoite-internal staining was observed that excluded the nucleus and was distinct from circumsporozoite (CS) protein staining, suggesting a cytoplasmic location.

See also the phenotype description of mutant RMgm-185 lacking expression of SAP1/SLARP and mutant RMgm-186 expressing an mCherry tagged version of SAP1/SLARP. For these mutants a nuclear location of SAP1/SLARP has been reported. Based on these observations it has been suggested that SAP1/SLARP functions as a specific regulator of the expression of genes involved at early steps of liver stage development

GenBank Accession No: EU652769.

Other mutants
RMgm-185: An independent mutant lacking expression of SAP1/SLARP
RMgm-186: A mutant expressing an mCherry tagged form of SAP1/SLARP