CHARACTERIZATION OF A 2ND LYSINE DECARBOXYLASE ISOLATED FROM ESCHERICHIA-COLI

We report here on the existence of a new gene for lysine decarboxylase in Escherichia coli K-12. The hybridization experiments with a cad4 p robe at low stringency showed that the homologous region of cadA was l ocated in lambda Kohara phage clone 6F5 at 4.7 min on the E. coli chro mosome. We cloned the 5.0-kb HindIII fragment of this phage clone and sequenced the homologous region of cadA. This region contained a 2,139 -nucleotide open reading frame encoding a 713-amino-acid protein with a calculated molecular weight of 80,589. Overexpression of the protein and determination of its N-terminal amino acid sequence defined the t ranslational start site of this gene. The deduced amino acid sequence showed 69.4% identify to that of lysine decarboxylase encoded by cadA at 93.7 min on tile E. coli chromosome. In addition, the level of lysi ne decarboxylase activity increased in strains carrying multiple copie s of the gene. Therefore, the gene encoding this lysine decarboxylase was designated ldc. Analysis of the lysine decarboxylase activity of s trains containing cad4, ldc, or cadA ldc mutations indicated that ldc was weakly expressed under various conditions but is a functional gene in E. coli.