Bacterial expression of PFV gag and pol genes. (A) Strategy to insert the gag and pol open reading frames into the bacterial expression vector pET22b. The FV gene fragments are placed in frame to a C-terminal histidine (HIS) tag. (RBS), prokaryotic ribosomal binding site. (B) Coomassie stain of recombinant proteins which were purified via the C-terminal HIS-tag over Ni2+-chelate matrices. Two examples per protein are shown.