Molecular cloning of the human methylthioadenosine phosphorylase processed pseudogene and localization to 3q28

Human methylthioadenosine phosphorylase (MTAP) is a purine and methionine metabolic enzyme present ubiquitously in all normal tissues, but often deleted in many types of cancer. The gene for this enzyme maps to chromosome 9 at band p21 where the cyclin-dependent kinase inhibitor genes for p16 and p15 also reside. During our efforts to clone this gene we also isolated a phage clone containing a processed pseudogene of MTAP. The sequence is 92% homologous to the MTAP cDNA, is flanked at its 3' end by a repetitive element, but does not possess a poly(A) stretch. We localized this processed pseudogene to band 28 on the long arm of chromosome 3 by fluorescence in situ hybridization. All 22 malignant cell lines with deletions at 9p21 screened possessed the pseudogene.