Expression of PML-RARα in TF1-S and TF1-L clones. Equal amounts of total cellular protein from nine independent TF1-S and TF1-L clones were immunoblotted with an antibody to human RARα, as detailed in Materials and Methods. Molecular weights are indicated to the left of the gel in kilodaltons (×10⁻³). The polyclonal RARα antibody detects both endogenous RARα (E, at approximately 55 kD), as well as the fusion PML-RARα proteins (S isoform, approximately 95 kD; L isoform, approximately 110 kD). The blots were stripped and reprobed with either MEK-2 or actin antibodies as a control for differences in loading and transfer.