The PML protein is a zinc finger transcription factor expressed as three major transcription products due to alternative splicing. The gene encoding human PML maps to chromosome 15q22. The t(15;17) (q22;q11.2-q12) chromosomal trans-location of the retinoic acid receptor alpha (RARalpha) gene occurs in virtually all cases of acute promyelocytic leukemia and results in the expression of a PML/RARalpha chimeric protein. Myeloid precursor cells expressing the PML/ RARalpha chimera fail to differentiate and exhibit an increased growth rate consequent to diminished apoptosis. PML/RARalpha transforms myeloid precursors by recruiting the nuclear co-repressor (N-CoR)-histone deacetylase complex that is essential to retinoic acid-dependent myeloid differentiation. PML/ RARalpha also recruits DNA methyltransferases in order to induce gene hypermethylation and silencing, which ultimately facilitates leukemogenesis.