SRSF4

PF3D7_1022400 (SRSF4) is a serine/arginine-rich protein of Plasmodium falciparum implicated in CLK-dependent pre-mRNA processing during the asexual blood stage (PMID:25188378). Its RS-rich domain is directly phosphorylated in vitro by all four parasite CLK kinases (PfCLK-1 through PfCLK-4), and this phosphorylation strictly requires the RS domain, since a peptide lacking it is not modified (PMID:25188378). Consistent with a role in nuclear RNA processing, the protein localizes predominantly to the nucleus of asexual blood stage trophozoites (PMID:25188378). Beyond identification as a CLK substrate and this nuclear localization, no direct functional experiments on SRSF4 itself have been characterized in the available corpus.

1. 2014 Medium

   To connect P. falciparum CLK kinases to a specific downstream substrate, it was shown that SRSF4's RS-rich domain is phosphorylated by all four PfCLKs, establishing SRSF4 as a physiological candidate effector of CLK signaling in the parasite.

   Evidence In vitro kinase assay with recombinant RS-domain-containing protein, with a domain-deletion peptide as negative control

   PMID:25188378

   Open questions at the time

   • Functional consequence of SRSF4 phosphorylation on splicing activity not tested
   • Which specific residues within the RS domain are phosphorylated not mapped
   • Whether each PfCLK acts on SRSF4 in vivo, or with distinct specificity, not resolved
2. 2014 Low

   To place SRSF4 in a cellular compartment consistent with a splicing role, subcellular fractionation/imaging showed it is predominantly nuclear in blood stage trophozoites.

   Evidence Subcellular localization assay in asexual blood stage trophozoites

   PMID:25188378

   Open questions at the time

   • Single localization method reported without a functional link specific to SRSF4
   • Nuclear sub-compartment (e.g. speckle-like association) not defined
   • Whether localization changes with phosphorylation state or across stages not tested

• Whether SRSF4 directly regulates pre-mRNA splicing, its target transcripts, and its requirement for parasite viability or development remain unknown.
• No RNA targets or splicing activity demonstrated for SRSF4
• No genetic knockout/knockdown phenotype established
• No structural or interaction data beyond CLK phosphorylation