On the evolution of the single-subunit RNA polymerases

J Mol Evol. 1997 Dec;45(6):671-81. doi: 10.1007/pl00006271.


Many eukaryotic nuclear genomes as well as mitochondrial plasmids contain genes displaying evident sequence similarity to those encoding the single-subunit RNA polymerase (ssRNAP) of bacteriophage T7 and its relatives. We have collected and aligned these ssRNAP sequences and have constructed unrooted phylogenetic trees that demonstrate the separation of ssRNAPs into three well-defined and nonoverlapping clusters (phage-encoded, nucleus-encoded, and plasmid-encoded). Our analyses indicate that these three subfamiles of T7-like RNAPs shared a common ancestor; however, the order in which the groups diverged cannot be inferred from available data. On the basis of structural similarities and mutational data, we suggest that the ancestral ssRNAP gene may have arisen via duplication and divergence of a DNA polymerase or reverse transcriptase gene. Considering the current phylogenetic distribution of ssRNAP sequences, we further suggest that the origin of the ancestral ssRNAP gene closely paralleled in time the introduction of mitochondria into eukaryotic cells through a eubacterial endosymbiosis.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • DNA-Directed RNA Polymerases / chemistry
  • DNA-Directed RNA Polymerases / genetics*
  • Evolution, Molecular*
  • Fungal Proteins / chemistry
  • Fungal Proteins / genetics*
  • Mitochondria / enzymology
  • Mitochondria / physiology
  • Molecular Sequence Data
  • Multigene Family*
  • Phylogeny
  • Plant Proteins / chemistry
  • Plant Proteins / genetics
  • Sequence Alignment
  • Viral Proteins / chemistry
  • Viral Proteins / genetics


  • Fungal Proteins
  • Plant Proteins
  • Viral Proteins
  • DNA-Directed RNA Polymerases

Associated data

  • GENBANK/AF000226