Additional remarks phenotype | Mutant/mutation
The mutant expresses a C-terminal mCherry-tagged version of a putative heptatricopeptide repeat protein (HPR) and expresses GFP under control of the hsp70 promoter
Protein (function)
The protein belongs to an organellar helical-hairpin-repeat protein family that was termed heptatricopeptide repeat (HPR) proteins
Phenotype
PBANKA_1436700::mCherry expression. Evidence for mitochondrial localisation in asexual blood stages and in gametocytes
Additional information
Transcription of the mitochondrial genome has been shown to lead to polycistronic transcripts, with mRNAs and rRNA fragments transcribed together as one precursor molecule. Even transcripts representing the entire genome have been detected. This expression organization suggests that post-transcriptional regulatory events, such as RNA processing, RNA stabilization, and RNA degradation, play an important role in mitochondria, similar to post-transcriptional gene regulation in the apicoplast. These processes are expected to require a large number of RNA-binding proteins (RBPs), but most of the components and mechanisms of the RNA-processing machinery remain unknown even in human mitochondria.All organellar RBPs must originate from the nuclear genome and be transferred to the organelles post-translationally. The largest class of organellar RBPs is helical-hairpin-repeat proteins called pentatricopeptide repeat proteins (PPRs). These proteins contain a tandem-repeat motif with up to 35 repetitions. Structurally, each repeat forms two alpha-helical elements that fold back onto each other. Alpha helices from consecutive repeats are stacked to form an extended RNA-interacting surface. Within this surface, each repeat is responsible for binding one base in a singlestranded RNA molecule. Two dedicated amino acids are key for specific RNA base recognition. Of the ∼450 predicted PPR proteins in Arabidopsis, approximately two thirds are localized to the mitochondria, with the remainder are found in the plastid. PPR proteins play an important role in RNA processing and transcript stabilization. Binding of a number of PPR proteins to mRNAs acts as a roadblock against exonucleolytic decay. Eventually, only small sequences that are protected by the PPR proteins remain; these can be detected by sequencing smallRNAs, providing a method for identifying PPR protein binding sites. A protein family with a set of functions and structure similar to PPR proteins, called the octatricopeptide repeat (OPR) family, is more prevalent in single-celled photosynthetic algae, e.g. Chlamydomonas reinhardtii. In Plasmodium, there are two annotated PPR proteins; one (PF3D7 1406400; PBANKA 1035800) is predicted to localize to the apicoplast and the other (PF3D7 1233300; PBANKA 1448000) to the mitochondrion. To our knowledge, no OPR proteins have been described in Apicomplexa to date. We discovered a novel helical-hairpin-repeat protein family distinct from PPR and OPR proteins, which we termed heptatricopeptide repeat (HPR) proteins, and demonstrated that individual HPRs are targeted to Plasmodium mitochondria. Although these proteins seem particularly abundant in apicomplexan parasites, they were also found in other species within the Alveolata. In fact, while they were not dected in bacteria, HPR proteins are found in most eukaryotic groups analyzed, including humans.
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