BACKGROUND: Splicing and alternate splicing are the two key biological processes 
that result in the generation of diverse transcript and protein isoforms in 
Plasmodium falciparum as well as in other eukaryotic organisms. Not much is 
known about the organization of splicing machinery and mechanisms in human 
malaria parasite. Present study reports the organization and assembly of 
Plasmodium spliceosome Sm core complex.
METHODS: Presence of all the seven Plasmodium Sm-like proteins in the 
intra-erythrocytic stages was assessed based on the protein(s) expression 
analysis using immuno-localization and western blotting. 
Localization/co-localization studies were performed by immunofluorescence 
analysis on thin parasite smear using laser scanning confocal microscope. 
Interaction studies were carried out using yeast two-hybrid analysis and 
validated by in vitro pull-down assays. PfPRMT5 (arginine methyl transferase) 
and PfSmD1 interaction analysis was performed by pull-down assays and the 
interacting proteins were identified by MALDI-TOF spectrometry.
RESULTS: PfSm proteins are expressed at asexual blood stages of the parasite and 
show nucleo-cytoplasmic localization. Protein-protein interaction studies showed 
that PfSm proteins form a heptameric complex, typical of spliceosome core 
complex as shown in humans. Interaction of PfSMN (survival of motor neuron, 
tudor domain containing protein) or PfTu-TSN (Tudor domain of Tudor 
Staphylococcal nuclease) with PfSmD1 proteins was found to be methylation 
dependent. Co-localization by immunofluorescence and co-immunoprecipitation 
studies suggested an association between PfPRMT5 and PfSmD1, indicating the role 
of arginine methylation in assembly of Plasmodium spliceosome complex.
CONCLUSIONS: Plasmodium Sm-like proteins form a heptameric ring-like structure, 
although the arrangement of PfSm proteins slightly differs from human splicing 
machinery. The data shows the interaction of PfSMN with PfSmD1 and this 
interaction is found to be methylation dependent. PfPRMT5 probably exists as a 
part of methylosome complex that may function in the cytoplasmic assembly of Sm 
proteins at asexual blood stages of P. falciparum.