Ribonucleotide reductases (RNRs) provide the only known de novo pathway for the biosynthesis of deoxyribonucleotides (dNTPs) for DNA synthesis and repair. RNRs catalyze the controlled reduction of all four ribonucleotides (NTPs) to maintain a balanced pool of dNTPs during the cell cycle and may constitute a rate-limiting step in chromosomal replication initiation. In prokaryotes RNR activity is controlled at two main levels. Nucleoside and deoxynucleoside triphosphate effector molecules allosterically regulate enzyme activity and specificity while equally important, though less well understood, is genetic regulation of enzyme activity. These processes enable the cell to rapidly adapt to changes in the intracellular replication machinery, to ensure faithful DNA replication and repair, and to respond to changes brought about by environmental factors, such as oxygen tension and oxidative stress agents. Three major classes of RNRs have been characterized. lass I RNRs are oxygen-dependent enzymes that occur in eubacteria, eukaryotes and some viruses, class II RNRs are oxygen-independent enzymes confined to bacteria, archaea, and a few unicellular eukaryotes, and class III RNRs are oxygen-sensitive enzymes present in anaerobes. Relatively little is known about how bacteria control RNR activity at the gene level. Studies of Streptomyces have shown that RNRs are regulated at the transcriptional level. Streptomyces spp. are gram-positive aerobic bacteria that produce a remarkable variety of metabolites and possess a complex life cycle. In Streptomyces coelicolor a transcriptional regulator, NrdR, controls expression of RNR genes, acting as transcriptional regulator by binding to tandem 16-bp sequences, termed NrdR-boxes, located in the upstream regulatory regions of both S. coelicolor RNR operons. Here you have a beautiful structure of the NdrR protein bound to a synthetic DNA containing the regulatory DNA sequence (PDB code: 7P3F)
#molecularart ... #immolecular ... #transcription ... #NdrR ... #regulation ... #DNA ... #regulationbox ... #cryoem
Structure of the protein-DNA complex rendered with @proteinimaging and depicted with @corelphotopaint
#molecularart ... #immolecular ... #transcription ... #NdrR ... #regulation ... #DNA ... #regulationbox ... #cryoem
Structure of the protein-DNA complex rendered with @proteinimaging and depicted with @corelphotopaint
