Identification of a putative Gag binding site critical for feline immunodeficiency virus genomic RNA packaging

Pr50^Gag specifically binds the FIV packaging signal RNA. (A) A representative gel of a band-shift assay performed using radiolabeled FIV gRNA (AD26) in the presence of increasing concentration of Pr50^Gag showing the formation of Pr50^Gag-radiolabeled gRNA complexes. (B,C) Band-shift competition assays showing the differential ability of unspliced WT gRNA (AD26) and spliced env mRNA (AD27) to displace Gag binding to the WT labeled gRNA (AD26). Briefly, a 744-nt long, radiolabeled, unspliced WT gRNA (AD26), and 400 nM FIV Pr50^Gag were incubated with increasing concentrations of unlabeled unspliced WT gRNA (AD26) or spliced env mRNA (AD27) as a competitor. The last lane shows the Proteinase K (ProK)-treated reaction mixture containing unspliced WT gRNA, 400 nM Pr50^Gag, and 400 nM competitor RNA. M and D denote the monomeric and dimeric forms of RNA, respectively.