Fig. 1

The Prototype Foamy Virus (PFV) genome, RNA transcripts, and protein products. a The molecular clone PFV-13 is depicted (Genbank accession no. U21247; 11,954 bp). The proviral long terminal repeats (LTR) are indicated at the 5′ and 3′ ends of the genome. Each LTR is composed of U3, R and U5 sequences. The U3 sequences are from the 3′ end of the viral RNA genome and the U5 sequences are from the 5′ end of the viral RNA genome. The R sequences are repeat sequences that are created during reverse transcription. Horizontal arrows indicate the location of the two viral promoters. The 5′ LTR promoter is blue and indicated as “P” while the internal promoter is green and indicated as “IP”. b The five major PFV mRNAs are shown. The first three mRNAs, including the unspliced genomic RNA and the spliced pol (polymerase) and env (envelope glycoprotein) mRNAs, are expressed from the 5′ LTR promoter and colored different shades of blue. The full-length unspliced RNA (light blue) serves as both the viral genome and the mRNA for the Gag (viral capsid) protein. The two smaller PFV mRNAs encoding the accessory proteins Tas (transactivator) and Bet proteins originate from the IP and are colored dark and light green, respectively. c The shaded boxes indicate the major PFV protein products, Gag, Pol and Env, as well as Tas and Bet. Viral protease-mediated cleavage sites within Gag and Pol are indicated with dashed lines and vertical arrows. The C-terminal P3 domain, released upon Gag cleavage, is indicated. The Pol protein contains PR, the protease domain, RT, the reverse transcriptase domain, and IN, the integrase domain. The Env protein is comprised of LP, leader peptide domain, SU, surface domain and TM, transmembrane domain