O. Francetic et al., The ChiA (YheB) protein of Escherichia coli K-12 is an endochitinase whosegene is negatively controlled by the nucleoid-structuring protein H-NS, MOL MICROB, 35(6), 2000, pp. 1506-1517
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.