MuPAR and HuPAR2 chimeras reveal regions required for PERV-A 14/220* infection. MuPAR is not permissive for PERV-A binding and entry, while HuPAR2 is permissive for both. Chimeras were constructed by swapping regions of HuPAR2 (solid black) with the corresponding residues of MuPAR (hatched black). Constructs were tagged with either an N-terminal c-myc tag (open circle) or a C-terminal eGFP tag (gray oval), as a way to monitor expression. Chimeras were expressed in non-permissive SIRC cells and tested for PERV-A infection. Levels of infection were determined by PERV pol qPCR of 250 ng genomic DNA and compared to wild-type HuPAR2 and MuPAR. (-/+) indicates the status of PERV-A infection. The average PERV pol copy numbers and standard deviations (n = 3) are shown for each. These chimeras revealed that the N-terminal 135 amino acids are critical for PERV-A 14/220* infection.