Fig 4. Analysis of PFV Gag phosphorylation status in purified virus particles.

PFV virions were produced by transient transfection of the four-component PFV vector system, containing the pcoPG4 variants denoted above each of the blots, into 293T cells. Viral particles were pelleted from cell-free tissue culture supernatants by ultracentrifugation through 20% sucrose and equal amounts of particle lysates separated by SDS-PAGE were blotted to nitrocellulose membranes. The phosphorylation status of the particle-associated Gag variants was determined by the corresponding antibodies specific for different phosphorylated amino acid motives as indicated. Data are representative of n = 4 independent experiments. (A) Schematic illustration of PFV Gag protein organization with highlighted putative T-P motifs and surrounding amino acids recognized when phosphorylated at the threonine residue by either the α-pT-P (orange letters) or α-Gag S-pT-P (blue letters) phosphopeptide-specific antibody. Solid vertical arrow: primary Gag processing site; dashed vertical arrows: secondary Gag processing sites; (B) Detection of the phosphorylated Thr-Pro (pT-P) motives in PFV Gag wt, iSTP and pmSTP virus particles (α-pT-P antiserum) and comparison with the total Gag content in the particle lysates (α-Gag). (C) Comparison of the pT-P phosphorylation status in the wt and T225A PFV particles in the absence (-) or presence (+) of the Lambda Phosphatase (λP) pretreatment of viral proteins. (D) Comparison of the PFV Gag-associated S-T-P motif phosphorylation status (α-Gag S-pT-P; detected with the corresponding PFV Gag-specific antibody) in virus preparations containing either the wt or the T225A Gag variant in the absence (-) or presence (+) of the λP pretreatment.