Establishment of BSAP/Pax5A-expressing EML cells. Parental EML cells (EML) were stably transfected with pPGKHygro and pPGKPax5A (the cDNA of Pax5A downstream of the PGK-1 promoter). Hygromycin-resistant cells were subcloned by limiting dilution and 5 μg of nuclear extract of individual clones containing pPGKPax5A detected by genomic PCR (M. Chiang and J. Monroe, unpublished observations) were subjected to EMSA with a³²P-end-labeled probe containing the high-affinity BSAP/Pax5A binding site isolated from the huCD19 promoter. (A) EML, parental wild-type EML; EML/Pax5A-2, -3, and -5, BSAP/Pax5A-expressing EML clones. (B) The intensity of the BSAP/Pax5A:probe complexes were quantitated using a densitometer.