Figure 1. The structure of PERV
a. The genomic DNA of PERVs includes both coding and non-coding sequences. The coding sequences of PERVs have three open reading frames (ORFs) to encode structural proteins (Gag), polymerase (Pol) and glycoprotein (Env), respectively. The non-coding sequences are called long terminal repeats (LTRs), localized on both sides of the ORFs. Each LTR contains a unique 3 (U3), repeat region (R), and unique 5 (U5) region.
b. The env gene encodes the proteins of the Env. It is synthesized as a single polyprotein, which is subsequently cleaved into two components: the surface subunit (SU) and the transmembrane envelope protein (TM). The receptor-binding domain (RBD) is localized on the N-terminus of the SU protein, while a highly conserved classical immunosuppressive domain (ISD) is situated in the TM domain.
c. Env spikes protein comprise trimers of three SU–TM multimers (only one is shown). The TM domain spans the membrane and anchors the entire complex in the surface of the virion or the host cells. During the maturation of the provirus, the TM protein is cleaved by PR to the p12E protein and R peptide.