Regulatory role of CsqR (YihW) in transcription of the genes for catabolism of the anionic sugar sulfoquinovose (SQ) in Escherichia coli K-12.

The binding sites of YihW, an uncharacterized DeoR-family transcription factor (TF) of Escherichia coli K-12, were identified using Genomic SELEX screening at two closely located sites, one inside the spacer between the bidirectional transcription units comprising the yihUTS operon and the yihV gene, and another one upstream of the yihW gene itself. Recently the YihUTS and YihV proteins were identified as catalysing the catabolism of sulfoquinovose (SQ), a hydrolysis product of sulfoquinovosyl diacylglycerol (SQDG) derived from plants and other photosynthetic organisms. Gel shift assay in vitro and reporter assay in vivo indicated that YihW functions as a repressor for all three transcription units. De-repression of the yih operons was found to be under the control of SQ as inducer, but not of lactose, glucose or galactose. Furthermore, a mode of its cooperative DNA binding was suggested for YihW by atomic force microscopy. Hence, as a regulator of the catabolism of SQ, we renamed YihW as CsqR.