Thymidine kinase of herpes virus as a vehicle for the isolation and characterization of unknown mammalian promoters and enhancers.

We have previously reported that the promoter of the thymidine kinase (TK) gene of herpes virus (HSV) can be replaced with the early promoter of SV40. In the present study we report the construction of a TK- plasmid (TK-pML-BglII) in which the TK promoter has been removed and a new BglII site has been regenerated for the insertion of exogenous promoters in front of this nonexpressed gene. We have tested the feasibility of using this plasmid for the isolation of unknown promoters by inserting DNA fragments containing the early and late promoters of human papovaviruses and have obtained activity. We have also inserted the fragments containing the 72-bp repeat enhancer sequences of SV40 and 107-bp repeat of the human BK virus into the intact TK plasmid (TK-pML) and observe increased frequency of transformation of mouse Ltk- cells to the TK+ phenotype. These results show that the TK system can be used as a vehicle for the isolation of unknown mammalian promoters and/or enhancers.