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The ChiA (YheB) protein of Escherichia coli K‐12 is an endochitinase whose gene is negatively controlled by the nucleoid‐structuring protein H‐NS
Author(s) -
Francetic˜ Olivera,
Badaut Cyril,
Rimsky Sylvie,
Pugsley Anthony P.
Publication year - 2000
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1046/j.1365-2958.2000.01817.x
Subject(s) - biology , escherichia coli , microbiology and biotechnology , nucleoid , gene , mutant , lac operon , fusion protein , transcription (linguistics) , gene expression , promoter , periplasmic space , reporter gene , genetics , recombinant dna , linguistics , philosophy
The chromosome of Escherichia coli K‐12 contains a putative gene, yheB ( chiA ), at centisome 74.7, whose product shows sequence similarity with chitinases of bacterial and viral origin. We cloned the chiA ( yheB ) gene and demonstrated that it codes for a 94.5 kDa periplasmic protein with endochitinase/lysozyme activity. Under standard laboratory growth conditions, chiA expression is very low, as shown by the Lac − phenotype of a chiA transcriptional fusion to a promoterless lacZ reporter. To identify factors that control chitinase gene expression, we generated random Tn 10 insertions in the chromosome of the fusion‐containing strain, selecting for a Lac + phenotype. The majority of the mutations that caused a Lac + phenotype mapped to the hns gene, encoding the nucleoid‐structuring protein H‐NS. Transcription of chiA in vivo is driven by a single σ 70 promoter and is derepressed in an hns mutant. Using a competitive gel retardation assay, we demonstrated that 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 regulatory proteins, such as fis , crp or stpA in combination with hns , increased chiA expression to different extents, as did decreasing the growth temperature from 37°C to 30°C. A possible physiological function of ChiA (YheB) endochitinase in E. coli K‐12 is discussed.