Schematic diagram of the retroviral vector pMSCVpac and a series of chimeric EG-R mutants.

EG-R (Y₇₀₄→F), (Y₇₂₉→F), (Y₇₄₄→F), (Y₇₆₄→F), and (Y_null) are mutant receptors with tyrosine substitution(s) as indicated; EG-R (P_{640, 642}→S) is a nonfunctional receptor with 2 amino acid substitutions as indicated. LTR, long terminal repeat; pgk, phosphoglycerate kinase; pac, puromycin N-acetyltransferase; TM, transmembrane.