Transduction assay on B-3T3 and N-3T3 cells. (A) Transduction of B-3T3 cells with Fv1b (left) and transduction of N-3T3 cells with Fv1n (right). Top row, B-tropic tester virus; middle row, N-tropic tester virus; bottom row, NB-tropic tester virus. (B) Transduction of B-3T3 cells with Fv1n (left) and transduction of N-3T3 cells with Fv1b (right). Top row, B-tropic tester virus; middle row, N-tropic tester virus; bottom row, NB-tropic tester virus.