As an initial step toward the cloning of a potential tumor suppressor gene at 12p12.3, we mapped the ETV6-CDKN1B region physically using bacterial artificial chromosome (BAC) and P1-derived clone (PAC) contigs.     ///    Methylation changes of the CpG islands in the ETV6-CDKN1B interval were assessed by Southern analysis for leukemia patients with hemizygous 12p deletions. 