Autoregulation of PurR repressor synthesis and involvement of purR in the regulation of pur B, purC, purL, purMN and guaBA expression in Escherichia coli

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Abstract
The pur R gene encodes a repressor (PurR) controlling the synthesis of the enzymes of purine biosynthesis. The subunit of PurR was identified as a 38‐kDa polypeptide by SDS/polyacrylamide gel electrophoresis. Analysis of a pur R–lacZ transcriptional fusion indicated that pur R expression is autoregulated. This was confirmed by gel retardation and DNasel footprinting experiments, where two PurR‐binding sites were identified in the transcribed part of pur R. Introduction of a purR mutation in wild‐type and pur – lac fusion strains was found to abolish purine repression of all genes of the purine biosynthetic pathway except for pur A.