RT-PCR analysis of peripheral blood of chimeric mice produced with EKLF−/− or EKLF−/−, LCRγ ES cells. Chimeras were generated by injecting EKLF−/− clones 2 and 6, and EKLF−/−, LCRγ clones 6-10 and 6-13 into C57BL/6J blastocysts. RNA was prepared from peripheral blood of eight chimeric mice at approximately 3 to 4 months of age and RT-PCR was performed using β-globin primers in the presence of ³²P-dCTP. The RT-PCR products were then digested with Msc I and separated on a 5% polyacrylamide gel, quantitated by phosphorimaging, and exposed to autoradiography. The 578-bp fragment represents the Msc I-resistant, β^single-globin RT-PCR product and the 487-bp fragment represents the Msc I-restricted, β^maj-, β^min-globin RT-PCR products (the 91-bp fragment was run off the gel to better resolve the 578 and 487 fragments). mRNAs from blood of C57BL/6J mice (Hbb^s/Hbb^s), 129Sv/Ev mice (Hbb^d/Hbb^d), and (C57BL/6J × CBA/J) F1 mice (Hbb^s/Hbb^d) were used as controls.