EFFECTS OF MULTICOPY LEUO ON THE EXPRESSION OF THE ACID-INDUCIBLE LYSINE DECARBOXYLASE GENE IN ESCHERICHIA-COLI

We previously reported that mutations in hns, the structural gene for the histone like protein H-NS, cause derepressed expression of cadA, w hich encodes the acid-inducible lysine decarboxylase at noninducing pH (pH 8.0). This study reports the characterization of a plasmid isolat ed from an Escherichia coli library that suppresses the effect of an h ns mutation on cadA expression. A previously sequenced open reading fr ame, leuO, proves to be the gene that causes the hns-complementing phe notype. The mechanism for this phenotype appears to be overexpression of leuO from a multicopy plasmid, which drastically reduces production of CadC, the essential activator for cadA induction, These results sh ow an in vivo regulatory phenotype for leuO, consistent with its propo sed protein sequence.