Mutant/mutation
The mutant lacks expression of S20 and expresses GFP under control of the constitutive eef1a promoter

Protein (function)
S20 orthologs are present in all Plasmodium species and a similar protein is found in T. gondii (TGGT1_229000). S20 orthologs are also present in other Coccidia, for instance Sarcocystis neurona (SRCN_6348), Besnoitia besnoiti (BESB_083580), Eimeria tenella (ETH_00029095), and Cyclospora cayetanensis (cyc_00626), but not Piroplasms. S20 proteins contain kelch motifs, segments of approximately 50 amino acid residues that form a single four-stranded, antiparallel beta-sheet. Kelch motifs are widely distributed in eukaryotic and prokaryotic proteins with divergent functions. The high degree of S20 protein sequence conservation among Plasmodium is indicative of a possible conserved function. The sequence of H2-Kb-restricted epitope VNYSFLYFL (Hafalla et al., 2013) is also relatively well maintained across Plasmodium species.
In a  high-content screen for CD8+ epitopes in the H2Kb/Db (C57BL/6)-restricted genetic background, S20 was identified with a distinct dominant epitope.

Phenotype
No phenotype detected throughout the complete life cycle

Additional information
Up-regulation of PbS20 mRNA in midgut and salivary gland sporozoites. Transcript levels dropped toward the end of liver stage maturation and remained low during blood infection.
Polyclonal anti-PbS20 peptide sera was generated. S20 could be detected in salivary gland sporozoites and in sporozoites that recently invaded hepatoma cells. However, 24 h after invasion, S20 was no longer detectable. The S20 antisera could only recognize S20 in sporozoites that had been permeabilized, which indicates that in contrast to CSP, S20 is restricted to the sporozoite interior. The specificity of the S20 signal in sporozoites was verified in immunofluorescence assays (IFAs) using s20(-) P. berghei, where no signal was detected.

From the Abstract:
'Protective immunity of irradiation-arrested s20(-) sporozoites in single, double and triple immunizations was similar to irradiated unaltered sporozoites in homologous challenge experiments. These findings demonstrate the presence of the immunogenic Plasmodium pre-erythrocytic determinant S20, which is not essential for eliciting protection. Although S20 is not needed for colonization of the mammalian host and for initiation of a blood infection, it is conserved amongst Plasmodium species. Malarial parasites express conserved, immunogenic proteins that are not required to establish infection but might play potential roles in diverting cellular immune responses.'

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