title: Targeting APOBEC3A to the viral nucleoprotein complex confers antiviral activity.
abstract: BACKGROUND
  APOBEC3 (A3) proteins constitute a family of cytidine deaminases that provide intracellular resistance to retrovirus replication and to transposition of endogenous retroelements. A3A has significant homology to the C-terminus of A3G but has only a single cytidine deaminase active site (CDA), unlike A3G, which has a second N-terminal CDA previously found to be important for Vif sensitivity and virus encapsidation. A3A is packaged into HIV-1 virions but, unlike A3G, does not have antiviral properties. Here, we investigated the reason for the lack of A3A antiviral activity.
  
  
  RESULTS
  Sequence alignment of A3G and A3A revealed significant homology of A3A to the C-terminal region of A3G. However, while A3G co-purified with detergent-resistant viral nucleoprotein complexes (NPC), virus-associated A3A was highly detergent-sensitive leading us to speculate that the ability to assemble into NPC may be a property conveyed by the A3G N-terminus. To test this model, we constructed an A3G-3A chimeric protein, in which the N-terminal half of A3G was fused to A3A. Interestingly, the A3G-3A chimera was packaged into HIV-1 particles and, unlike A3A, associated with the viral NPC. Furthermore, the A3G-3A chimera displayed strong antiviral activity against HIV-1 and was sensitive to inhibition by HIV-1 Vif.
  
  
  CONCLUSIONS
  Our results suggest that the A3G N-terminal domain carries determinants important for targeting the protein to viral NPCs. Transfer of this domain to A3A results in A3A targeting to viral NPCs and confers antiviral activity.
authors.affiliation: Laboratory of Molecular Microbiology, Viral Biochemistry Section, National Institute of Allergy and Infectious Diseases, NIH, Building 4, Room 310, 4 Center Drive, MSC 0460, Bethesda, MD 20892-0460, USA. rgaur@niaid.nih.gov
authors.forename: Ritu
authors.initials: R
authors.lastname: Goila-Gaur
authors.forename: Mohammad A
authors.initials: MA
authors.lastname: Khan
authors.forename: Eri
authors.initials: E
authors.lastname: Miyagi
authors.forename: Sandra
authors.initials: S
authors.lastname: Kao
authors.forename: Klaus
authors.initials: K
authors.lastname: Strebel
mesh_terms: D000595:Amino Acid Sequence; D003564:Cytidine Deaminase / Q000378:metabolism*; D016346:Gene Products, vif / Q000235:genetics / Q000378:metabolism*; D015658:HIV Infections / Q000201:enzymology* / Q000235:genetics / Q000276:immunology / Q000821:virology; D015497:HIV-1 / Q000235:genetics / Q000378:metabolism / Q000472:pathogenicity / Q000502:physiology*; D006367:HeLa Cells; D006801:Humans; D015151:Immunoblotting; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D008969:Molecular Sequence Data; D009698:Nucleoproteins / Q000378:metabolism*; D011506:Proteins / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D016415:Sequence Alignment; D013347:Subcellular Fractions / Q000378:metabolism; D014162:Transfection; D014779:Virus Replication; D054320:vif Gene Products, Human Immunodeficiency Virus
chemical_list: D016346:Gene Products, vif; D009698:Nucleoproteins; D011506:Proteins; D011993:Recombinant Fusion Proteins; D054320:vif Gene Products, Human Immunodeficiency Virus; C121399:APOBEC3A protein, human; D003564:Cytidine Deaminase