S-methyl-5'-thioadenosine phosphorylase is an enzyme that in humans is encoded by the MTAP gene. This gene encodes an enzyme that plays a major role in polyamine metabolism and is important for the salvage of both adenine and methionine. The encoded enzyme is deficient in many cancers because this gene and the tumor suppressor p16 gene are co-deleted. Multiple alternatively spliced transcript variants have been described for this gene, but their full-length natures remain unknown. The encoded enzyme is deficient in many cancers because this gene and the tumor suppressor p16 gene are co-deleted. Multiple alternatively spliced transcript variants have been described for this gene, but their full-length natures remain unknown.