FUNCTIONAL-ANALYSIS OF THE ESCHERICHIA-COLI K-12 CYN OPERON TRANSCRIPTIONAL REGULATION

The cynTSX operon enables Escherichia coli K-12 to degrade and use cya nate as a sole nitrogen source. The promoter of this operon is positiv ely regulated by cyanate and the CynR protein. CynR, a member of the L ysR family of regulatory proteins, binds specifically to a 136-bp DNA fragment containing both the cynR and the cynTSX promoters. In this st udy, we report the results of DNase I digestion studies showing that C ynR protects a 60-bp region on the cynR coding strand and a 56-bp sequ ence on the cynTSX coding strand. CynR binding was not affected by cya nate or its structural homolog azide, a gratuitous inducer of the oper on. However, CynR-induced bending of two different DNA fragments was d etected. The amount of bending was decreased by cyanate.