Detection of A889T by ASO hybridization in case no. 2. Using a control sample (ATRA-sensitive APL cells with a short PML/RARα isoform) (lanes 1 and 3) and case no. 2 (lanes 2 and 4), DNA segments amplified differentially from RARα (lanes 1 and 2) or PML/RARα chimeric gene (lanes 3 and 4). (A) Ethidium bromide staining of agarose gel electrophoresis. (B) The membrane blotted from (A) was hybridized with oligonucleotide probe specific for the wild-type sequence. (C) The membrane same as (B) was hybridized with oligonucleotide probe for A889T. The sequence of wild-type probe was 5′-CGGACCCAGATGCACAACGC-3′, the center adenine of which was replaced with thymidine in the mutant probe. The mutant probe positively hybridized only to the DNA segment that was amplified from PML/RARα chimeric gene of case no. 2 (lane 4).