Molecular analyses revealed the presence and transcription of transgenes in leukemic cells. (Top) Scheme of both proviruses encoding the MLL·AF4 and AF4·MLL alleles. (Left panels) Genomic PCR experiments of 4 primary leukemic mice, displaying the results of leukemic cells that either encode the AF4·MLL transgene and developed a pro-B or a B/T BAL disease phenotype or that exhibit both t(4;11) fusion alleles and developed a B/T BAL or mixed lineage leukemia (MLL). Neg indicates negative control; Pos, positive control; and gDNA, genomic DNA isolated from the leukemic cells of indicated mice. (Right panels) RT-PCR analysis of 3 mice representing the pro-B, B/T BAL, and MLL leukemia disease phenotype. Appropriate controls (−RT) demonstrated that only cDNA derived from total RNA was investigated (+RT). Transcription of all transgenes was demonstrated. GAPDH indicates positive control for isolated RNA; P, PIDE::MLL·AF4 or PIDE::AF4·MLL plasmids served as positive controls; N, negative control; BM, bone marrow, wild type; and M, DNA size marker (lambda DNA, ClaI digested).