Construction of plasmid vectors for cloning of promoters using the dihydrofolate reductase gene of Escherichia coli K-12.

Vectors for cloning promoter-DNA fragments were derived from pTP 30-5 which was constructed in our previous work (M. Iwakura et al. (1982) J. Biochem. 91, 1205). The selection was based on the expression of trimethoprim resistance of transformed bacteria in which the enhancement of dihydrofolate reductase production was directed by the cloned promoter. A linear relationship between the content of dihydrofolate reductase and the strength of trimethoprim resistance was observed. It is suggested that the promoter activities can be estimated by trimethoprim resistance without measuring the enzyme activities.