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Exonuclease-mediated degradation of nascent RNA

[Abstract]:
AntigenicvariationofthePlasmodiumfalciparummulticopyvargenefamilyenablesparasiteevasionofimmunedestructionbyhostantibodies1,2.Expressionofaparticularvarsubgroup,termedupsA,islinkedtotheobstructionofbl
Antigenic variation of the Plasmodium falciparum multicopy var genefamilyenablesparasiteevasionofimmunedestructionbyhost antibodies 1,2 .Expressionofaparticular var subgroup,termed upsA ,islinkedtotheobstructionofbloodvesselsinthebrainandtothepath-ogenesisofhumancerebralmalaria 3–6 .Themechanismdetermining upsA activation remains unknown. Here we show that an entirely
new type of gene silencing mechanism involving an exonuclease-mediateddegradationofnascentRNAcontrolsthesilencingofgenes linked to severe malaria. We identify a novel chromatin-associated exoribonuclease, termed PfRNaseII, that controls the silencing of upsAvar genesbymarkingtheirtranscriptionstartsiteandintron-promoterregionsleadingtoshort-livedcrypticRNA.Parasitescarry-
ingadeficient PfRNaseII geneproducefull-length upsAvar transcripts andintron-derivedantisenselongnon-codingRNA.Thepresenceof stable upsA var transcripts overcomes monoallelic expression, re-sultinginthesimultaneousexpressionofboth upsA and upsC type PfEMP1 proteins on the surface of individual infected red blood cells. 
lencegenesinvolvedinpathogenesisinpatientswithseveremalaria may provide new strategies for reducing malaria mortality