Fusion of the Escherichia coli tRNALeu1 promoter to the galK gene: analysis of sequences necessary for growth-rate-dependent regulation.

We have fused DNA fragments derived from an Escherichia coli tRNALeu1 operon to the galK gene of E. coli to identify sequences necessary for the in vivo initiation of transcription and growth-rate-dependent regulation. Promoter sequences consisting of residues from -50 to +56 or -50 to +5 with respect to the in vivo site for initiation of transcription were introduced into chimeric plasmids upstream from the galK gene. Cells bearing these chimeric plasmids exhibited much higher levels of galactokinase than did cells bearing plasmids wherein the galactose promoter was fused to galK. This indicates that the tRNALeu1 promoter is substantially more efficient than the gal promoter. The tRNALeu1 promoter-galK chimeras exhibited marked growth-dependent regulation in a manner consistent with that reported for tRNA regulation. Since tRNALeu1 DNA spanning residues -50 to +5 was sufficient to provide growth rate regulation of galK, an inverted repeat centered at position +17 is not, under the conditions we used, required for this type of regulation.