Using in silico analysis, the yciW gene of Eschetichia coil was identified as a novel L-cysteine regulon that may be regulated by the transcriptional activator CysB for sulfur metabolic genes. We found that overexpression of yciW conferred tolerance to L-cysteine, but disruption of yciW increased L-cysteine production in E. coli. (C) 2014, The Society for Biotechnology, Japan. All rights reserved.