(A) Structure of the retroviral vectors used to transduce murine bone marrow. The LTRs and vector backbone for all constructs was MSCV2.2. The EcoRI and Xba I restriction enzyme sites used for determining proviral integration are indicated. (B) Protocol for retroviral transduction of FU-treated bone marrow and subsequent reconstitution. During the 48-hour cocultivation, retroviral supernatants were added to the media (1 mL every 24 hours) or cells were transduced by spin infection without cocultivation (see Materials and Methods).