SUMO (Small Ubiquitin-like MOdifier) conjugation is a post-translational 
modification implicated in a variety of cellular functions including 
transcriptional regulation, nuclear location and signal transduction. 
Sumoylation, although conserved and vital in eukaryotes, has not been studied in 
malaria parasites. Here, we identify SUMO conjugation of blood stage parasites 
of Plasmodium falciparum. Antibodies raised against synthetic peptides of the 
plasmodial SUMO orthologue PfSUMO, a 100-amino-acid protein, reacted with 
distinctive subcellular compartments of the parasitized erythrocyte during blood 
stage development. Anti-PfSUMO stains the nucleus and parasite cytoplasm. We 
also found antibody reactivity in the host cell cytoplasm with the 
parasite-derived structures called Maurer's clefts. Anti-PfSUMO reacts in 
Western blot with a number of blood stage proteins ranging from approximately 
40-250 kDa. Parasites expressing FLAG-tagged PfSUMO gave similar results in 
Immunofluorescence assay and Western blots. In addition, we show that 
anti-PfSUMO identified PfSir2, a telomere-associated nuclear protein involved in 
var gene silencing, as a target for sumoylation. Furthermore, LC-MS/MS analysis 
of a two-step immunoprecipitation (IP) with anti-FLAG and anti-PfSUMO antibodies 
reveals a number of putative P. falciparum sumoylated proteins. Our results 
imply that SUMO conjugation has an essential function in a number of different 
biological processes in P. falciparum.