Mutant/mutation
The mutant expresses a C-terminal GFP-tagged version of of ORP1. The gfp::orp1 expression cassette is introduced into the (silent) small subunit ribosomal rna gene (c/d-type unit). The ORP1 N-terminal 365 amino acids is fused to GFP.

Protein (function)
In the paper it is shown that each of two HFD (histone-fold domain)-containing proteins of P. berghei gene (IDs PBANKA_0902500 and PBANKA_1303400), which are named oocyst rupture protein 1 (ORP1) and ORP2, have essential and similar functions in the rupture of the oocyst capsule. Evidence is presented that protein interaction via the HFD is critical for function. ORP1 is located in the oocyst capsule, whereas ORP2 is re-localized from the oocyst cytoplasm to the capsule at the time when mature sporozoites have formed.
The histone-fold domain (HFD) is found in histones and in proteins with a role in transcriptional regulation such as the TATA-box-binding protein-associated factor TAFII and in the CCAAT-binding transcription factor subunits NF-YB and NF-YC. The only example of a protein with a HFD acting outside the nucleus is son-of-sevenless, a protein with multiple domains containing two HFDs, which are involved in binding to lipids. The HFD is B70 amino acids in length and forms three helices separated by small linker sequences. In a heterodimer the proteins are organized in head-to-tail orientation, resulting in a compact ‘handshake’ interaction. In the well-studied NF-Y complex, the heterodimer NF-YB and NF-YC interacts with a third subunit, NF-YA. Although the heterodimer binds DNA in a nonspecific manner, the NF-YA subunit confers binding specificity to the CCAAT motif.
ORP1 (PBANKA_0902500, 950 amino acids) contains a carboxyterminal HFD. ORP2 has an amino-terminal HFD, which is most similar to NF-YC of plants and animals, and HAP5 of yeast. Both HFDs comprises the three a-helices characteristic of the HFD and the short aC helix found in NF-YB/NF-YC proteins. Neither of the two proteins contains any other recognizable motifs and outside the HFD there is only a low degree of similarity comparing the two. The two proteins are considerably longer than NF-YB and NF-YC of animals. BLAST searches of the Plasmodium genome failed to reveal any protein with similarity to NF-YA, which suggested that these two proteins may not be part of a classical NF-Y DNA-binding complex.

Phenotype
Phenotype analyses of a mutant lacking ORP1 (PBANKA_0902500) indicates a role in realease of sporozoites from the oocyst (see RMgm-4059)

In ookinetes and sporozoites the ORP1::GFP protein was detected in the cytoplasm but not in the nucleus, whereas in the oocyst stage ORP1 was found in the periphery of the mature cyst. Double-labelling experiments revealed that ORP1::GFP co-localizes with the protein Cap380 (PBANKA_1218100), a protein of the oocyst capsule.

Additional information
See RMgm-4059 for a mutant lacking ORP1 (PBANKA_0902500).
See RMgm-4060 for a mutant lacking ORP2 (PBANKA_1303400).
See RMgm-4061 for a mutant with a mutated histone-fold domain (HFD) of ORP1. Phenotype analyses of this mutant indicates that HFD is essential for ORF function
See RMgm-4063 for a mutants expresing  a mCherry-tagged version of ORP2. Analyses of these mutants show  that ORP1 is located in the oocyst capsule, whereas ORP2 is re-localized from the oocyst cytoplasm to the capsule at the time when mature sporozoites have formed.

Other mutants
See above