STRINGENT AND GROWTH-RATE-DEPENDENT CONTROL OF THE GUA OPERON OF ESCHERICHIA-COLI K-12

The promoter of the gua operon has been located by transcript mapping using primer extension with reverse transcriptase. The surrounding nuc leotide sequence has features characteristic of promoters under string ent and growth-rate-dependent regulation, namely a GC-rich discriminat or next to the -10 hexamer, an upstream AT-rich sequence (the UP eleme nt) and potential FIS-binding sites. Transcriptional activity of the g ua promoter was examined using transcriptional fusions to lacZ placed at a single chromosomal location. Expression from gua was reduced unde r stringent conditions in vivo, and varied with growth rate. Growth-ra te control was independent of guanine-mediated repression. A fusion in which the GC-rich discriminator was mutated by insertion of an AT-ric h oligonucleotide was used to demonstrate the importance of this regio n in control. Both stringent and growth-rate-dependent controls were a bolished by the mutation, Other potential regulatory signals in the vi cinity of the gua promoter are a pur operator (binding site for the Pu rR repressor), a gua operator, a DnaA-binding site and a CRP/FNR-bindi ng sequence. the gua promoter lies back-to-back with the promoter for xseA (exonuclease VII), the two promoters being separated by only 20 b p.