title: Production of infectious human immunodeficiency virus type 1 does not require depletion of APOBEC3G from virus-producing cells.
abstract: BACKGROUND
  The human immunodeficiency virus Vif protein overcomes the inhibitory activity of the APOBEC3G cytidine deaminase by prohibiting its packaging into virions. Inhibition of APOBEC3G encapsidation is paralleled by a reduction of its intracellular level presumably caused by the Vif-induced proteasome-dependent degradation of APOBEC3G.
  
  
  RESULTS
  In this report we employed confocal microscopy to study the effects of Vif on the expression of APOBEC3G on a single cell level. HeLa cells dually transfected with Vif and APOBEC3G expression vectors revealed efficient co-expression of the two proteins. Under optimal staining conditions approximately 80% of the transfected cells scored double-positive for Vif and APOBEC3G. However, the proportion of double-positive cells observed in identical cultures varied dependent on the fixation protocol and on the choice of antibodies used ranging from as low as 40% to as high as 80% of transfected cells. Importantly, single-positive cells expressing either Vif or APOBEC3G were observed both with wild type Vif and a biologically inactive Vif variant. Thus, the lack of APOBEC3G in some Vif-expressing cells cannot be attributed to Vif-induced degradation of APOBEC3G. These findings are consistent with our results from immunoblot analyses that revealed only moderate effects of Vif on the APOBEC3G steady state levels. Of note, viruses produced under such conditions were fully infectious demonstrating that the Vif protein used in our analyses was both functional and expressed at saturating levels.
  
  
  CONCLUSIONS
  Our results suggest that Vif and APOBEC3G can be efficiently co-expressed. Thus, depletion of APOBEC3G from Vif expressing cells as suggested previously is not a universal property of Vif and thus is not imperative for the production of infectious virions.
authors.affiliation: Laboratory of Molecular Microbiology, National Institute of Allergy and Infectious Diseases, NIH, Building 4, Room 310, 4 Center Drive, MSC 0460, Bethesda, MD 20892-0460, USA. skao@niaid.nih.gov
authors.forename: Sandra
authors.initials: S
authors.lastname: Kao
authors.forename: Eri
authors.initials: E
authors.lastname: Miyagi
authors.forename: Mohammad A
authors.initials: MA
authors.lastname: Khan
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Takeuchi
authors.forename: Sandrine
authors.initials: S
authors.lastname: Opi
authors.forename: Ritu
authors.initials: R
authors.lastname: Goila-Gaur
authors.forename: Klaus
authors.initials: K
authors.lastname: Strebel
mesh_terms: D000071480:APOBEC-3G Deaminase; D003001:Cloning, Molecular; D003564:Cytidine Deaminase / Q000235:genetics; D016346:Gene Products, vif / Q000276:immunology / Q000502:physiology; D006679:HIV Seropositivity / Q000821:virology; D015497:HIV-1 / Q000235:genetics* / Q000472:pathogenicity*; D006367:HeLa Cells; D006801:Humans; D018613:Microscopy, Confocal; D009700:Nucleoside Deaminases / Q000235:genetics*; D011401:Promoter Regions, Genetic; D012097:Repressor Proteins / Q000235:genetics*; D017384:Sequence Deletion; D014771:Virion / Q000502:physiology; D054320:vif Gene Products, Human Immunodeficiency Virus
chemical_list: D016346:Gene Products, vif; D012097:Repressor Proteins; D054320:vif Gene Products, Human Immunodeficiency Virus; D009700:Nucleoside Deaminases; D000071480:APOBEC-3G Deaminase; C464924:APOBEC3G protein, human; D003564:Cytidine Deaminase