Transcriptional analysis of a locus involved in LPS biosynthesis and transport to the outer membrane of E. coli

The outer membrane (OM) of Gram-negative bacteria is an asymmetric lipid bilayer that interacts with the environment and helps preserving the cell integrity. Lipopolysaccharide (LPS) is the major essential component of the OM. Although its structure and biosynthesis are well known, the transport mechanism of this molecule from the inner membrane to the OM are poorly understood. We previously showed that all genes except yrbG in a locus composed of yrbG-kdsD-kdsC-lptC-lptA-lptB are involved in LPS biosynthesis and transport and obtained genetic evidence that at least three promoters are scattered within this locus. We now analyzed in more detail the transcriptional organization of the locus. The picture emerging is that this region seems to be transcribed from five promoters: yrbGp, kdsCp1, kdsCp2, lptAp1 and lptAp2, with different sigma factors implicated in their regulation. This complex transcriptional organization suggests that the different genes of this locus may be finely and differentially regulated. Work is in progress to understand which environmental conditions may modulate the expression patterns of these genes.