The LipB protein is a negative regulator of dam gene expression in Escherichia coli

Transcription initiation of the major promoter (P2) of the Escherichia coli dam gene increases with growth rate. The presence of three partially palin dromic motifs, (TTCAGT(N-20)TGAG), designated G (growth)-boxes, within the -52 to +31 region of the promoter, may be related to growth rate control. D eletion of two of these repeats, downstream of the transcription initiation point, result in constitutive high activity of the promoter. The unlinked cde-l::miniTn10 insertion also results in severalfold higher activity of th e darn P2 promoter, suggesting that this mutation resulted in the loss of a putative dam P2 repressor. The cde-4 mutation was mapped to the lipB (lipo ic acid) gene, which we show encodes a 24 kDa protein initiating at a TTG c odon. LipB is a highly conserved protein in animal and plant species, other bacteria, Archaea, and yeast. Plasmids expressing the native or hexahistid ine-tagged LipB complement the phenotype of the cde-l mutant strain. The le vel of LipB in vivo was higher in exponentially growing cells than those in the stationary phase. Three G-box motifs were also found in the lipB regio n. Models for the regulation of expression of the two genes are discussed. (C) 2000 Elsevier Science B.V. All rights reserved.