CONTRIBUTION OF THE P-MRA PROMOTER TO EXPRESSION OF GENES IN THE ESCHERICHIA-COLI MRA CLUSTER OF CELL-ENVELOPE BIOSYNTHESIS AND CELL-DIVISION GENES

Recently, a promoter for the essential gene ftsI, which encodes penici llin-binding protein 3 of Escherichia coli, was precisely localized 1. 9 kb upstream from this gene, at the beginning of the mra cluster of c ell division and cell envelope biosynthesis genes (H. Hara, S. Yasuda, K. Horiuchi, and J. T. Park, J. Bacteriol. 179:5802-5811, 1997). Disr uption of this promoter (P-mra) on the chromosome and its replacement by the lac promoter (P-mra::P-lac) led to isopropyl-beta-D-thiogalacto pyranoside (IPTG)-dependent cells that lysed in the absence of inducer , a defect which was complemented only when the whole region from P-mr a to ftsW, the fifth gene downstream from ftsI, was provided in trans on a plasmid, In the present work, the levels of various proteins invo lved in peptidoglycan synthesis and cell division were precisely deter mined ill cells in which P-mra::P-lac promoter expression was represse d or fully induced. It was confirmed that the P-mra promoter is requir ed for expression of the first nine genes of the mva cluster: mraZ (or fC), mraW (OrfB), ftSL (mraR), ftsI, murE, murF, mraY, murD, and ftsW, Interestingly, three- to sixfold-decreased levels of MurG and MurC en zymes were observed in uninduced P-mra::P-lac cells, This was correlat ed with an accumulation of the nucleotide precursors UDP-N-acetylgluco samine and UDP-N-acetylmuramic acid, substrates of these enzymes, and viith a depletion of the pool of UDP-N-acetylmuramyl pentapeptide, res ulting in decreased cell wall peptidoglycan synthesis. Moreover, the e xpression of ftsZ, the penultimate gene from this cluster, was signifi cantly reduced when P-mra expression was repressed, It was concluded t hat the transcription of the genes located downstream from ftsW in the mra cluster, from murG to ftsZ, is also mainly (but not exclusively) dependent on the P-mra promoter.