Schematic structure of PML-RAR mRNA showing the major functional domains. The PML portion is hatched and the RAR portion is clear. Numbers in the boxes indicate exons. Vertical arrows indicate the positions of break/fusion sites in the translocated PML gene that result in the formation of three different forms of PML-RAR mRNA: S-, V-, and L-forms. Arrowheads show the sites of PCR primers used in this study. Primers used for screening of the PML region are shown beneath the schematic bar, whereas those for the RAR region are shown above it. The asterisks indicate the positions of base changes found in the PML-RAR allele, and the coding region amino acid changes are shown in expanded form below the schematic bar. The abbreviations are as follows: Pro, proline-rich domain; Cys, cysteine/histidine clusters; -Helix, -helical coiled-coil dimerization domain; B-F, B- to F-region of RAR; ZF, zinc-finger RING motif; BB1 and BB2, two B-boxes; DBD, DNA binding domain; DD, dimerization domain; LBD, ligand binding domain; AF-2, activator function-2 domain; AF-2 AD CORE, 7 amino acid long AF-2 activation domain; 3′-UT, 3′ untranslated region.