Fig 7.

Model of the mechanisms by which PuuR regulates puu gene expression. At low intracellular putrescine concentrations, PuuR binds to the intergenic region between puuA and puuD and represses the expression of the puu genes. At high intracellular putrescine concentrations, PuuR dissociates from DNA, and transcription of the puu genes occurs. At least some of the transcripts are expressed as mRNA-puuAP and mRNA-puuDRCBE together from the puuA and puuD promoters, respectively. Circled PuuR indicates PuuR protein. The horizontal thick black arrows indicate the puu gene cluster. White arrows between puuA and puuD indicate the puuA and puuD promoters. The expressions of mRNAs from each promoter are shown by fine arrows below the gene names. The vertical black arrows indicate shifts of intracellular putrescine concentration.