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1rlr A:10-221 PDB entry domain
|Cross references ||IPR008926 SSF48168 Protein matches|
The large subunit (R1) of ribonucleotide reductase (RNR), is an essential enzyme required for DNA replication and DNA repair. In both Escherichia coli and higher organisms, the enzyme consists of two non-identical subunits, a dimer of an 85-kDa protein, R1, and a dimer of a 45-kDa protein, R2. Both subunits are essential for RNR enzyme activity - R1 contains, in the substrate binding site, the reducing active cysteine pair and R2 provides a catalytically essential organic radical. R1 is able to bind and reduce the four common ribonucleoside diphosphates. Substrate specificity is determined by nucleoside triphosphates binding to a protein site different from the active site and acting as allosteric effectors. Thus the presence of ATP makes the enzyme reduce CDP and UDP, dGTP favours ADP reduction and dTTP favours GDP reduction. dATP is a general inhibitor. This provides a mechanism for a balanced enzymatic production of building blocks for DNA synthesis .
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