Polar allele duplication for transcriptional analysis of consecutive essential genes: application to a cluster of Escherichia coli fatty acid biosynthetic genes.

The genes encoding acyl carrier protein and several key fatty acid biosynthetic enzymes are clustered at min 24 of the Escherichia coli chromosome. This cluster of genes is not transcribed as a classical operon, but rather multiple promoters are present and each gene is cotranscribed with at least one other gene. Transcripts specific for single genes ar also present. Transcription of acpP, the gene encoding acyl carrier protein, has been studied in detail. The acpP gene was shown to be transcribed from at least two different promoters by Northern (RNA) blot, primer extension, and deletion analyses, and the major promoter was mapped. We tested whether multiple promoters are necessary to produce acyl carrier protein by use of a new method whereby a transcriptional terminator was integrated into the chromosome upstream of the intact acpP gene. By use of this method (called polar allele duplication), we demonstrate that the promoter located immediately upstream of the coding sequence is sufficient for synthesis of this very abundant protein.