title: U1snRNP-mediated suppression of polyadenylation in conjunction with the RNA structure controls poly (A) site selection in foamy viruses.
abstract: BACKGROUND
  During reverse transcription, retroviruses duplicate the long terminal repeats (LTRs). These identical LTRs carry both promoter regions and functional polyadenylation sites. To express full-length transcripts, retroviruses have to suppress polyadenylation in the 5'LTR and activate polyadenylation in the 3'LTR. Foamy viruses have a unique LTR structure with respect to the location of the major splice donor (MSD), which is located upstream of the polyadenylation signal.
  
  
  RESULTS
  Here, we describe the mechanisms of foamy viruses regulating polyadenylation. We show that binding of the U1 small nuclear ribonucleoprotein (U1snRNP) to the MSD suppresses polyadenylation at the 5'LTR. In contrast, polyadenylation at the 3'LTR is achieved by adoption of a different RNA structure at the MSD region, which blocks U1snRNP binding and furthers RNA cleavage and subsequent polyadenylation.
  
  
  CONCLUSIONS
  Recently, it was shown that U1snRNP is able to suppress the usage of intronic cryptic polyadenylation sites in the cellular genome. Foamy viruses take advantage of this surveillance mechanism to suppress premature polyadenylation at the 5'end of their RNA. At the 3'end, Foamy viruses use a secondary structure to presumably block access of U1snRNP and thereby activate polyadenylation at the end of the genome. Our data reveal a contribution of U1snRNP to cellular polyadenylation site selection and to the regulation of gene expression.
authors.affiliation: Institute of Virology and Immunobiology, University of Würzburg, Würzburg, Germany.
authors.forename: Eva-Maria
authors.initials: EM
authors.lastname: Schrom
authors.forename: Rebecca
authors.initials: R
authors.lastname: Moschall
authors.forename: Maximilian J
authors.initials: MJ
authors.lastname: Hartl
authors.forename: Helena
authors.initials: H
authors.lastname: Weitner
authors.forename: David
authors.initials: D
authors.lastname: Fecher
authors.forename: Jörg
authors.initials: J
authors.lastname: Langemeier
authors.forename: Jens
authors.initials: J
authors.lastname: Bohne
authors.forename: Birgitta M
authors.initials: BM
authors.lastname: Wöhrl
authors.forename: Jochen
authors.initials: J
authors.lastname: Bodem
mesh_terms: D000818:Animals; D002460:Cell Line; D006224:Cricetinae; D009690:Nucleic Acid Conformation; D011061:Poly A / Q000378:metabolism*; D026723:Polyadenylation; D039104:RNA 3' Polyadenylation Signals; D022821:RNA Splice Sites; D012342:RNA, Small Nuclear / Q000378:metabolism*; D012367:RNA, Viral / Q000737:chemistry* / Q000378:metabolism*; D016092:Spumavirus / Q000502:physiology*; D020079:Terminal Repeat Sequences
chemical_list: D022821:RNA Splice Sites; D012342:RNA, Small Nuclear; D012367:RNA, Viral; C405483:U1 small nuclear RNA; D011061:Poly A