The short, four-helical domain first identified in the Plasmodium export proteins PHISTa and PHISTc has been extended to become this six-helical PRESAN domain identified in the P. falciparum-specific RESA-type (Ring-infected erythrocyte surface antigen) proteins in association with the DnaJ domain. Overall, at least 67 proteins have been detected in P. falciparum with complete copies of the PRESAN domain. No versions of this domain were detected in other apicomplexan genera, suggesting that the domain was 'invented' after the divergence of the lineage leading to the genus Plasmodium undergoing a dramatic proliferation only in P. falciparum. A secondary structure-prediction derived from the multiple alignment of the PRESAN family reveals that it is composed of an all-helical fold with six conserved helical segments. There is some evidence it might localize to membranes.