Molecular analysis and identification of the TBLR1-RARα fusion transcript. (A) Partial sequence analysis of the TBLR1-RARα transcript. TBLR1 exon 5 was fused to exon 3 of RARα. The junction site of TBLR1 and RARα is highlighted by a bold arrowhead. The TBLR1-RARα encodes an in-frame fusion transcript; its partial DNA sequence and the corresponding translated amino acid sequence are shown. (B) RT-PCR analysis of TBLR1-RARα fusion transcript and reciprocal RARα-TBLR1 fusion transcript. TBLR1-RARα fusion transcript (lane 3) was amplified from cDNA derived from the patient 1’s BMMNCs at diagnosis with an internal control (GAPDH) by RT-PCR, whereas the reciprocal RARα-TBLR1 fusion transcript (lane 5) was not detected. cDNA derived from K562 was used as a negative control. (C) Amplification of full-length TBLR1-RARα by RT-PCR. Full-length TBLR1-RARα was also detected from patient 1’s BM samples. (D) Schematic representation of TBLR1, RARα, and TBLR1-RARα proteins. TBLR1-RARα fusion protein contains 545 amino acids (aa), including a LisH domain (6-32 aa) in the TBLR1 portion and a DNA-binding domain (DBD; 166-250 aa) and a ligand-binding domain (LBD; 270-500 aa) in the RARα portion. The break point is indicated by the red line. (E) RT-PCR analysis of TBLR1-RARα fusion transcripts in the other 2 APL patients harboring t(3;17) chromosomal translocation. TBLR1-RARα fusion transcripts (lanes 2 and 3) were amplified from cDNAs derived from the APL patients’ BMMNCs at diagnosis with an internal control (GAPDH) by RT-PCR. cDNA derived from K562 was used as a negative control, and cDNA derived from K562 transfected with TBLR1-RARα (K562-TR) was used as a positive control.