Escherichia coli WC196, which was obtained from the strain W3110 by nitrosoguanidine mutagenesis as an overproducer of lysine, produced approximately twenty times more cadaverine than did W3110, and had a twenty fold higher level of rpoS gene product, σ³⁸, than in W3110. Both WC196 and W3110 had a stop codon (TAG) in rpoS at position which corresponds to the 33th residue of σ³⁸ protein. In addition, WC196 but not W3110 had a mutation in the gene encoding Ser-tRNA (SerU), called, supD. Analysis of the amino acid sequence of a σ³⁸ preparation from WC196 showed that the 33th residue of σ³⁸ is a serine residue. The ΔrpoS ΔcadA mutant of E. coli W3110 harboring the plasmid containing rpoS, in which the TAG codon was converted to a TCG codon for serine-33 residue of σ³⁸, expressed a significant amount of Ldc and accumulated a large amount of σ³⁸. However, the ΔrpoS ΔcadA mutant of W3110 with the plasmid containing the intact rpoS from W3110 could synthesize neither σ³⁸ nor Ldc significantly.

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