title: Recruitment of PfSET2 by RNA polymerase II to variant antigen encoding loci contributes to antigenic variation in P. falciparum.
abstract: Histone modifications are important regulators of gene expression in all eukaryotes. In Plasmodium falciparum, these epigenetic marks regulate expression of genes involved in several aspects of host-parasite interactions, including antigenic variation. While the identities and genomic positions of many histone modifications have now been cataloged, how they are targeted to defined genomic regions remains poorly understood. For example, how variant antigen encoding loci (var) are targeted for deposition of unique histone marks is a mystery that continues to perplex the field. Here we describe the recruitment of an ortholog of the histone modifier SET2 to var genes through direct interactions with the C-terminal domain (CTD) of RNA polymerase II. In higher eukaryotes, SET2 is a histone methyltransferase recruited by RNA pol II during mRNA transcription; however, the ortholog in P. falciparum (PfSET2) has an atypical architecture and its role in regulating transcription is unknown. Here we show that PfSET2 binds to the unphosphorylated form of the CTD, a property inconsistent with its recruitment during mRNA synthesis. Further, we show that H3K36me3, the epigenetic mark deposited by PfSET2, is enriched at both active and silent var gene loci, providing additional evidence that its recruitment is not associated with mRNA production. Over-expression of a dominant negative form of PfSET2 designed to disrupt binding to RNA pol II induced rapid var gene expression switching, confirming both the importance of PfSET2 in var gene regulation and a role for RNA pol II in its recruitment. RNA pol II is known to transcribe non-coding RNAs from both active and silent var genes, providing a possible mechanism by which it could recruit PfSET2 to var loci. This work unifies previous reports of histone modifications, the production of ncRNAs, and the promoter activity of var introns into a mechanism that contributes to antigenic variation by malaria parasites.
authors.affiliation: Department of Microbiology and Immunology, Weill Medical College of Cornell University, New York, New York, United States of America.
authors.forename: Uchechi E
authors.initials: UE
authors.lastname: Ukaegbu
authors.affiliation: Department of Microbiology and Immunology, Weill Medical College of Cornell University, New York, New York, United States of America.
authors.forename: Sandeep P
authors.initials: SP
authors.lastname: Kishore
authors.affiliation: Department of Microbiology and Immunology, Weill Medical College of Cornell University, New York, New York, United States of America.
authors.forename: Dacia L
authors.initials: DL
authors.lastname: Kwiatkowski
authors.affiliation: Program in Computational Biology, Weill Medical College of Cornell University, New York, New York, United States of America.
authors.forename: Chethan
authors.initials: C
authors.lastname: Pandarinath
authors.affiliation: Department of Microbiology and Molecular Genetics, The Institute for Medical Research Israel-Canada, The Kuvin Center for the Study of Infectious and Tropical Diseases, Hebrew University-Hadassah Medical School, Jerusalem, Israel.
authors.forename: Noa
authors.initials: N
authors.lastname: Dahan-Pasternak
authors.affiliation: Department of Microbiology and Molecular Genetics, The Institute for Medical Research Israel-Canada, The Kuvin Center for the Study of Infectious and Tropical Diseases, Hebrew University-Hadassah Medical School, Jerusalem, Israel.
authors.forename: Ron
authors.initials: R
authors.lastname: Dzikowski
authors.affiliation: Department of Microbiology and Immunology, Weill Medical College of Cornell University, New York, New York, United States of America.
authors.forename: Kirk W
authors.initials: KW
authors.lastname: Deitsch
mesh_terms: D000940:Antigenic Variation / Q000502:physiology*; D000953:Antigens, Protozoan / Q000235:genetics / Q000276:immunology*; D044127:Epigenesis, Genetic / Q000276:immunology; D000076983:Histone Methyltransferases; D011495:Histone-Lysine N-Methyltransferase / Q000235:genetics / Q000276:immunology*; D006801:Humans; D010963:Plasmodium falciparum / Q000235:genetics / Q000276:immunology*; D015800:Protozoan Proteins / Q000235:genetics / Q000276:immunology*; D012319:RNA Polymerase II / Q000235:genetics / Q000276:immunology*; D012333:RNA, Messenger / Q000235:genetics / Q000276:immunology; D016053:RNA, Protozoan / Q000235:genetics / Q000276:immunology
chemical_list: D000953:Antigens, Protozoan; D015800:Protozoan Proteins; D012333:RNA, Messenger; D016053:RNA, Protozoan; C085731:erythrocyte membrane protein 1, Plasmodium falciparum; D000076983:Histone Methyltransferases; D011495:Histone-Lysine N-Methyltransferase; D012319:RNA Polymerase II