Detection of G815A mutation by Pst I digestion in case no. 1. DNA segments amplified differentially from RARα in lanes 1 through 4 or from PML/RARα chimeric gene in lanes 5 through 8. Lanes 1 and 3, HL-60; lanes 5 and 7, an ATRA-sensitive control patient harboring a short PML/RARα isoform; lanes 2, 4, 6, and 8, case no. 1. PCR products in lanes 2, 4, 6, and 8 were digested with Pst I before electrophoresis. The Pst I digestion pattern of RARα-derived segments in case no. 1 (lanes 3 and 4) was similar to that of HL-60 (lanes 1 and 2). By contrast, the 873-bp segment derived from PML/RARα in case no. 1 was digested with Pst I into three fragments due to two Pst I sites including one additional site (lanes 7 and 8), which was not detected in a control patient without mutation (lanes 5 and 6).