From RNA to DNA, why so many ribonucleotide reductases?

Science. 1993 Jun 18;260(5115):1773-7. doi: 10.1126/science.8511586.


It is generally accepted that DNA appeared after RNA during the chemical evolution of life. To synthesize DNA, deoxyribonucleotides are required as building blocks. At present, these are formed from the corresponding ribonucleotides through the enzymatic action of ribonucleotide reductases. Three classes of enzymes are present in various organisms. There is little sequence similarity among the three classes of reductases. However, enzymic mechanisms and the allosteric behavior of the enzymes from various organisms are strongly conserved, suggesting that the enzymes might have evolved from a common ancestor, with the class III anaerobic Escherichia coli reductase as its closest relative.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Allosteric Regulation
  • Amino Acid Sequence
  • Anaerobiosis
  • Biological Evolution
  • Cobamides / metabolism
  • Cysteine / chemistry
  • Escherichia coli / enzymology
  • Iron / metabolism
  • Lactobacillus / enzymology
  • Molecular Sequence Data
  • Oxidation-Reduction
  • Ribonucleotide Reductases / chemistry
  • Ribonucleotide Reductases / metabolism*
  • Ribonucleotides / metabolism*
  • Substrate Specificity
  • Tyrosine / metabolism


  • Cobamides
  • Ribonucleotides
  • Tyrosine
  • Iron
  • Ribonucleotide Reductases
  • cobamamide
  • Cysteine