[Role of additional binding sites for the CytR protein in the regulation of Escherichia coli udp gene expression].

The nucleotide sequence of a 1000-bp fragment of the Escherichia coli chromosome located between genes metE and udp and including the promoter region of the udp gene was determined. Multiple binding sites for the CytR and CRP proteins were identified outside the canonical udp gene promoter. A set of deletion variants with the truncated regulatory region of the udp gene was isolated based on plasmids pSKII and pJEL250. The level of CytR regulation of the udp gene was shown to depend on the size of the regulatory region relative to the transcription initiation site. On the basis of these data, it is concluded that additional binding sites for the CytR protein located in the regulatory region are functionally active in the regulation of udp gene expression. This conclusion has been confirmed by properties of the udp264 promoter mutant, which contains a deletion covering the main CytR binding site within the canonical promoter. Irrespective of the deletion, the expression of the udp gene in mutant udpP264 retains the dependence on the allelic state of the cytR gene. The CytR protein was shown to act as a transcription repressor or activator, depending on the configuration of the promoter and on the relative location and quantity of binding sites for CytR and CRP proteins.