The association of thymidine kinase activity and thymidine transport in Escherichia coli

We have constructed a series of mutants within the putative nucleoside-binding site of the herpes simplex type-1 virus (HSV-1) thymidine kinase (TK)-encoding gene ( tk ), contained within an expression vector. While most mutations within this sequence produce an inactive protein, we find no absolute requirement for the wild-type He 166 and Ala 167 . The uptake of thymidine (dT) into Escherichia coli tdk − , lacking functional endogenous TK activity, is proportional to the amount of TK activity expressed from the heterologous HSV-1 tk gene. In contrast, there is no enhancement in deoxycytidine uptake into E. coli producing (HSV-1) TK. These results imply a specific role for TK in the active transport of dT into E. coli .