High expression of the second lysine decarboxylase gene, ldc, in Escherichia coli WC196 due to the recognition of the stop codon (TAG), at a positionwhich corresponds to the 33th amino acid residue of sigma(38), as a serineresidue by the amber suppressor, supD

Escherichia coil WC196, which was obtained from the strain W3110 by nitroso guanidine mutagenesis as an overproducer of lysine, produced approximately twenty times more cadaverine than did W3110, and had a twenty fold higher l evel of rpoS gene product, sigma(38), than in W3110. Both WC196 and W3110 h ad a stop codon (TAG) in rpoS at position which corresponds to the 33th res idue of sigma(38) protein. In addition, WC196 but not W3110 had a mutation in the gene encoding Ser-tRNA (SerU), called, supD. Analysis of the amino a cid sequence of a sigma(38) preparation from WC196 showed that the 33th res idue of sigma(38) is a serine residue, The Delta rpoS Delta cadA mutant of E. coil W3110 harboring the plasmid containing rpoS, in which the TAG codon was converted to a TCG codon for serine-33 residue of sigma(38), expressed a significant amount of Ldc and accumulated a large amount of sigma(38). H owever, the Delta rpoS Delta cadA mutant of W3110 with the plasmid containi ng the intact rpoS from W3110 could synthesize neither sigma(38) nor Ldc si gnificantly.