The ChiA (YheB) protein of Escherichia coli K-12 is an endochitinase whosegene is negatively controlled by the nucleoid-structuring protein H-NS

The chromosome of Escherichia coli K-12 contains a putative gene, yheB (chi A), at centisome 74.7, whose product shows sequence similarity with chitina ses of bacterial and viral origin. We cloned the chiA (yheB) gene and demon strated that it codes for a 94.5 kDa periplasmic protein with endochitinase /lysozyme activity. Under standard laboratory growth conditions, chiA expre ssion is very low, as shown by the Lac(-) phenotype of a chiA transcription al fusion to a promoterless lacZ reporter. To identify factors that control chitinase gene expression, we generated random Tn10 insertions in the chro mosome of the fusion-containing strain, selecting for a Lac(+) phenotype. T he majority of the mutations that caused a Lac(+) phenotype mapped to the h ns gene, encoding the nucleoid-structuring protein H-NS. Transcription of c hiA in vivo is driven by a single sigma(70) promoter and is derepressed in an hns mutant. Using a competitive gel retardation assay, we demonstrated t hat H-NS binds directly and with high affinity to the chiA promoter region. In addition to hns, other E. coli mutations causing defects in global regu latory proteins, such as fis, crp or stpA in combination with hns, increase d chiA expression to different extents, as did decreasing the growth temper ature from 37 degrees C to 30 degrees C. A possible physiological function of ChiA (YheB) endochitinase in E. coli K-12 is discussed.