Two RpoT genes of Physcomitrella patens encode phage-type RNA polymerases with dual targeting to mitochondria and plastids

Gene. 2002 May 15;290(1-2):95-105. doi: 10.1016/s0378-1119(02)00583-8.


Angiosperms possess a small family of phage-type RNA polymerase genes that arose by gene duplication from an ancestral gene encoding the mitochondrial RNA polymerase. We have isolated and sequenced the genes and cDNAs encoding two phage-type RNA polymerases, PpRpoT1 and PpRpoT2, from the moss Physcomitrella patens. PpRpoT1 comprises 19 exons and 18 introns, PpRpoT2 contains two additional introns. The N-terminal transit peptides of both polymerases are shown to confer dual-targeting of green fluorescent protein fusions to mitochondria and plastids. In vitro translation of the cDNAs revealed initiation of translation at two in-frame AUG start codons. Translation from the first methionine gives rise to a plastid-targeted polymerase, whereas initiation from the second methionine results in exclusively mitochondrial-targeted protein. Thus, dual-targeting of Physcomitrella RpoT is caused by and might be regulated by multiple translational starts. In phylogenetic analyses, the Physcomitrella RpoT polymerases form a sister group to all other phage-type polymerases of land plants. The two genes result from a gene duplication event that occurred independently from the one which led to the organellar polymerases with mitochondrial or plastid targeting properties in angiosperms. Yet, according to their conserved exon-intron structures they are representatives of the molecular evolutionary line leading to the RpoT genes of higher land plants.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Bryopsida / enzymology
  • Bryopsida / genetics*
  • Cloning, Molecular
  • DNA, Plant / chemistry
  • DNA, Plant / genetics
  • DNA, Plant / isolation & purification
  • DNA-Directed RNA Polymerases / genetics*
  • DNA-Directed RNA Polymerases / metabolism
  • Exons
  • Genes, Plant / drug effects
  • Green Fluorescent Proteins
  • Introns
  • Isoenzymes / genetics
  • Luminescent Proteins / genetics
  • Luminescent Proteins / metabolism
  • Microscopy, Confocal
  • Mitochondria / enzymology*
  • Molecular Sequence Data
  • Phylogeny
  • Plant Proteins / genetics*
  • Plastids / enzymology*
  • Protein Biosynthesis
  • RNA, Messenger / genetics
  • Recombinant Fusion Proteins / genetics
  • Recombinant Fusion Proteins / metabolism
  • Sequence Alignment
  • Sequence Analysis, DNA
  • Sequence Homology, Amino Acid


  • DNA, Plant
  • Isoenzymes
  • Luminescent Proteins
  • Plant Proteins
  • RNA, Messenger
  • Recombinant Fusion Proteins
  • Green Fluorescent Proteins
  • DNA-Directed RNA Polymerases

Associated data

  • GENBANK/AJ416854
  • GENBANK/AJ416855