Part of the salvage pathway for purine and pyrimidine deoxyribonucleotide synthesis. Phosphorylates preferentially purines over pyrimidines. ATP + thymidine = ADP + dTMP + H(+) kcat is 0.045 sec(-1) with deoxyuridine (dU) as substrate. kcat is 0.02 sec(-1) with deoxythymidine (dT) as substrate. kcat is 0.009 sec(-1) with 3'-azido-3'-deoxythymidine (AZT) as substrate. Purine metabolism. Pyrimidine metabolism. Dimer. No visible phenotype. The double mutant tk1a tk1b is seedling lethal. Belongs to the thymidine kinase family. Truncated N-terminus.