ESCHERICHIA-COLI THYMIDINE KINASE - NUCLEOTIDE-SEQUENCE OF THE GENE AND RELATIONSHIPS TO OTHER THYMIDINE KINASES

The thymidine kinase (TK)-encoding gene (tdk) of Escherichia coli is located at min 27 of the E. coli genetic map. Sequence analysis of this region revealed an open reading frame of 205 codons. Identification of this region as the E. coli tdk gene was confirmed by its similarity to other TK-encoding genes. The E. coli amino acid (aa) sequence showed significant similarity to the corresponding TK polypeptides of vertebrates and large DNA viruses, but showed no similarity to known herpesvirus TK enzymes. Mapping of highly conserved positions among all sequences indicates the importance of these residues for catalytic activity and may facilitate further functional studies. Using a distance matrix method, the evolutionary relationships among the TK aa sequences of poxviruses, eukaryotes and prokaryotes were analyzed and a potential phylogenetic tree was established.