Functional domains of the PML protein and structure of the PML-RAR and reciprocal RAR-PML proteins generated in t(15;17)-APL. In all patients, the RING finger, B boxes, and at least the first two coiled coil domains of PML are included in the fusion protein. Heterogeneity in the breakpoint within the PML gene leads to a long and short form of PML-RAR depicted, as well as the rarer intermediate form (not shown). The RAR-PML fusion is detected in the majority of cases, but no evident function can be ascertained from its structure.