Mutant/mutation
The mutant expresses a (C-terminal) FLAG-tagged version of SEP1. The endogenous sep1 gene is not tagged. The FLAG-tagged copy of sep1 is introduced into the genome into the (silent) c/d-ssu-rRNA locus. The FLAG-tagged copy of sep1 is under the control of the upstream and downstream regulatory regions of the endogenous sep1.

Protein (function)
Early transcribed membrane protein (ETRAMP) family member. Plasmodium conserved family with greater than ten members in P. falciparum. ETRAMPs are abundantly expressed early in the intraerythrocytic cycle and are small (frequently less than 200 aa) integral membrane proteins that are localized within the parasitophorous vacuolar membrane (PVM). All members have signal peptides plus a transmembrane domain. The ETRAMP/SEP proteins of P. yoelii and P. berghei (8-11 genes) show homology to members of the ETRAMP family of proteins of P. falciparum (14 genes) but the orthologous relationship of the different members is not completely resolved.

P. berghei sep genes, Pbsep1, Pbsep2 and Pbsep3 (PBANKA_052480, PBANKA_052420 and PBANKA_050110, respectively) are 3 ETRAMP members which reside in the subtelomeric regions of chromosome 5. The three genes share the upstream regulatory region and differ in their 3’UTRs. The encoded proteins (13-16 KDa) are nearly identical in the first 81 amino acids, which include a predicted signal peptide, a lysine-rich domain and a TM region, while differ in their C-terminal portion.
Mutants lacking expression of SEP1 have been generated (RMgm-16, RMgm-18) which show a normal phenotype during the complete life cycle, comparable to wild type parasites.
Multiple attempts to disrupt sep2 en sep3 (RMgm-64, RMgm-65) indicate that these proteins are essential for blood stage proliferation.
SEP1 is an integral membrane of the parasitophorous vacuole membrane of blood stages.

Phenotype
The phenotype has not been analysed in detail. Antibodies against SEP1 recognized the endogenous SEP1 in Western analysis. However, these antibodies failed to recognise the FLAG-tagged version of SEP1 (SEP1-F). This might be be explained by the fact that the immune serum was raised against the C-terminal peptide (18 amino acids) of SEP1 and the fusion with FLAG may have affected its conformation. As expected, α-FLAG monoclonal antibody detected SEP1-F.

See RMgm-680 and RMgm-681 for more detailed analyses of mutants expressing FLAG-tagged SEP2 and SEP3, showing transport of SEP2 and SEP3 into the cytoplasm of the host erythrocyte. In the paper additional analyses are shown for determination of motifs for export of these proteins.

Additional information
SEP2 and SEP3 are components of the parasitophorous vacuole membrane (PVM). During blood stage development vesicle-like structures containing these proteins detach from the PVM en route to the host cytosol. These SEP-containing vesicles remain associated with the infected erythrocyte ghosts most probably anchored to the membrane skeleton.

Other mutants
See RMgm-680 and RMgm-681 for more detailed analyses of mutants expressing FLAG-tagged SEP2 and SEP3