Retroviral vectors MPL-PURO, MML-PURO, and gene transfer efficiency.

(A) pMPL-PURO contains the same MPL cassette used in SNV-MPL with the difference that in this vector the cassette is under the transcriptional control of the viral LTR. The puromycin resistance gene (puro) is translated from an IRES (provided by J. Zhang) and was placed 3′ of the MPL cassette. Southern blotting was performed on genomic DNA from MPL-PURO–infected 3T3 cells, MPL-PURO cocultivated primary spleen B cells, and a 0.5 copy number control as indicated. (B) pMML-PURO contains the MML chimeric gene under the transcriptional control of the viral LTR and the puro gene, which is translated from IRES. Southern blotting was performed on genomic DNA extracted from MML-PURO–infected 3T3 cells, MML-PURO cocultivated primary spleen B cells, and a 0.5 copy number control as indicated.