The tumor suppressor promyelocytic leukemia (PML) protein is fused to the 
retinoic acid receptor alpha in patients suffering from acute promyelocytic 
leukemia (APL). Treatment of APL patients with arsenic trioxide (As2O3) reverses 
the disease phenotype by a process involving the degradation of the fusion 
protein via its PML moiety. Several PML isoforms are generated from a single PML 
gene by alternative splicing. They share the same N-terminal region containing 
the RBCC/tripartite motif but differ in their C-terminal sequences. Recent 
studies of all the PML isoforms reveal the specific functions of each. Here, we 
review the nomenclature and structural organization of the PML isoforms in order 
to clarify the various designations and classifications found in different 
databases. The functions of the PML isoforms and their differential roles in 
antiviral defense also are reviewed. Finally, the key players involved in the 
degradation of the PML isoforms in response to As2O3 or other inducers are 
discussed.