Relative activities of the transcriptional regulatory sites in the rplKAJLrpoBC gene cluster of Escherichia coli.

The pattern of transcription of the rplKAJLrpoBC gene cluster of Escherichia coli appears to be complex. At least four different promoters and a transcriptional attenuator have been identified. To compare the relative effect of each of the putative promoters and the attenuator on transcription of these genes, we fused these regulatory sites to lacZ. These transcriptional fusions were constructed on lambda transducing phages so a single copy of each could be stably integrated into the chromosome. The level of beta-galactosidase in a lysogen of each phage reflects the activity of the transcriptional regulatory site. We find that the promoters preceding rplK (rplKp) and rplJ (rplJp) are indeed the major promoters of this gene cluster. The minor promoter before rplL (rplLp) is much weaker and contributes little to the transcription of the downstream genes. Under these conditions, we find no evidence of a promoter (rpoBp) in the rplL-rpoB intercistronic region. The attenuator (atn) terminates ca. 70% of the transcripts initiated at the promoters preceding it. Although we cannot rule out that some transcripts from rplKp may read through into rplJLrpoBC, we find that rplJp alone is sufficient for high-level expression of these genes.