REGULATION OF ESCHERICHIA-COLI GLNB, PRSA, AND SPEA BY THE PURINE REPRESSOR

A strategy was devised to identify Escherichia coli genes subject to c oregulation by purR. From a data base search, similarities to the pur regulon cis-acting control site were found in 26 E. coli genes. Of fiv e genes examined in which the putative pur operator is upstream of the coding sequence, glnB, prsA, and speA bound purified purine repressor in vitro. Binding of the repressor to a pur operator in these genes w as dependent upon a corepressor. The pur operator in glnB is located b etween two major transcription start sites that were located by primer extension mapping. The effect of purR on expression of glnB, prsA, an d speA was examined by using a lacZ reporter. The results indicated tw o- to threefold repression of these genes by purR. Coregulation by pur R provides evidence that expands the pur regulon to include glnB, prsA , and speA. These genes have functions related to nucleotide metabolis m.