title: A functional conserved intronic G run in HIV-1 intron 3 is critical to counteract APOBEC3G-mediated host restriction.
abstract: BACKGROUND
  The HIV-1 accessory proteins, Viral Infectivity Factor (Vif) and the pleiotropic Viral Protein R (Vpr) are important for efficient virus replication. While in non-permissive cells an appropriate amount of Vif is critical to counteract APOBEC3G-mediated host restriction, the Vpr-induced G2 arrest sets the stage for highest transcriptional activity of the HIV-1 long terminal repeat.
  
  
  RESULTS
  We identified a G run localized deep in the vpr AUG containing intron 3 (GI3-2), which was critical for balanced splicing of both vif and vpr non-coding leader exons. Inactivation of GI3-2 resulted in excessive exon 3 splicing as well as exon-definition mediated vpr mRNA formation. However, in an apparently mutually exclusive manner this was incompatible with recognition of upstream exon 2 and vif mRNA processing. As a consequence, inactivation of GI3-2 led to accumulation of Vpr protein with a concomitant reduction in Vif protein. We further demonstrate that preventing hnRNP binding to intron 3 by GI3-2 mutation diminished levels of vif mRNA. In APOBEC3G-expressing but not in APOBEC3G-deficient T cell lines, mutation of GI3-2 led to a considerable replication defect. Moreover, in HIV-1 isolates carrying an inactivating mutation in GI3-2, we identified an adjacent G-rich sequence (GI3-1), which was able to substitute for the inactivated GI3-2.
  
  
  CONCLUSIONS
  The functionally conserved intronic G run in HIV-1 intron 3 plays a major role in the apparently mutually exclusive exon selection of vif and vpr leader exons and hence in vif and vpr mRNA formation. The competition between these exons determines the ability to evade APOBEC3G-mediated antiviral effects due to optimal vif expression.
authors.forename: Marek
authors.initials: M
authors.lastname: Widera
authors.forename: Frank
authors.initials: F
authors.lastname: Hillebrand
authors.forename: Steffen
authors.initials: S
authors.lastname: Erkelenz
authors.forename: Ananda Ayyappan Jaguva
authors.initials: AA
authors.lastname: Vasudevan
authors.forename: Carsten
authors.initials: C
authors.lastname: Münk
authors.forename: Heiner
authors.initials: H
authors.lastname: Schaal
mesh_terms: D000071480:APOBEC-3G Deaminase; D002460:Cell Line; D045744:Cell Line, Tumor; D003564:Cytidine Deaminase / Q000235:genetics / Q000378:metabolism*; D016336:Gene Products, vpr / Q000235:genetics; D057809:HEK293 Cells; D015658:HIV Infections / Q000378:metabolism / Q000821:virology*; D015497:HIV-1 / Q000235:genetics*; D006367:HeLa Cells; D058507:Host Specificity / Q000235:genetics*; D006801:Humans; D007438:Introns; D009154:Mutation / Q000235:genetics; D012326:RNA Splicing / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics; D013601:T-Lymphocytes / Q000378:metabolism / Q000821:virology; D014779:Virus Replication / Q000235:genetics; D054320:vif Gene Products, Human Immunodeficiency Virus / Q000235:genetics; D054325:vpr Gene Products, Human Immunodeficiency Virus / Q000235:genetics
chemical_list: D016336:Gene Products, vpr; D012333:RNA, Messenger; D054320:vif Gene Products, Human Immunodeficiency Virus; D054325:vpr Gene Products, Human Immunodeficiency Virus; D000071480:APOBEC-3G Deaminase; C464924:APOBEC3G protein, human; D003564:Cytidine Deaminase