Thymidine Kinase 2, Mitochondrial (TK2)

TK2 encodes a deoxyribonucleoside kinase that specifically phosphorylates thymidine, deoxycytidine, and deoxyuridine. The encoded enzyme localizes to the mitochondria and is required for mitochondrial DNA synthesis. Mutations in this gene are associated with a myopathic form of mitochondrial DNA depletion syndrome. Alternate splicing results in multiple transcript variants.
The gene encodes a 234-amino acid polypeptide. Although TK2 is believed to reside in mitochondria, it contains no mitochondrial translocation signal sequence. Northern blot analysis revealed that TK2 was ubiquitously expressed as 2 transcripts of 2.4 and 4 kb. Expression of the TK2 cDNA resulted in a 60-kD protein.