Human thymidine kinase gene: molecular cloning and nucleotide sequence of a cDNA expressible in mammalian cells

A cDNA containing the entire coding region of the human thymidine kinase gene has been molecularly cloned. The cDNA is under the control of a simian virus 40 promoter and is expressible in mammalian cells. The complete nucleotide sequence of the human thymidine kinase cDNA has been determined. The cDNA is 1,421 base pairs in length and has a large open reading frame of 702 base pairs capable of specifying a protein with a molecular weight of 25,504. Genomic Southern blotting experiments show that sequences homologous to the human thymidine kinase cDNA are conserved among many vertebrates, including prosimians (lemur), tree shrews, rats, mice, and chickens. Direct comparison of the nucleotide sequences of the human thymidine kinase cDNA and the chicken thymidine kinase gene reveals ca. 70% overall homology. This homology is extended further at the amino acid sequence level, with greater than 74% amino acid residues matched between the human and chicken thymidine kinase proteins.