Non-AUG translation initiation of mRNA encoding plastid-targeted phage-type RNA polymerase in Nicotiana sylvestris

Biochem Biophys Res Commun. 2002 Nov 22;299(1):57-61. doi: 10.1016/s0006-291x(02)02579-2.


A third nuclear gene encoding a bacteriophage T7-type RNA polymerase, NsRpoT-C, was isolated and characterized from Nicotiana sylvestris. The gene, NsRpoT-C, consists of 21 exons and 20 introns and encodes a polypeptide of 977 amino acid residues. The predicted NsRpoT-C protein shows the highest identity (72% amino acid identity) with Arabidopsis thaliana RpoT;3 which is a plastid-targeted protein. Surprisingly, comparison of the deduced amino acid sequence of NsRpoT-C with that of A. thaliana RpoT;3 predicted that the NsRpoT-C starts at a CUG triplet, a rare translation initiation codon. Transient expression assays in protoplasts from tobacco leaves demonstrated that the putative N-terminal transit peptide of NsRpoT-C encodes a targeting signal directing the protein into chloroplasts. This strongly suggests that NsRpoT-C functions as an RNA polymerase transcribing plastid-encoded genes. We have designated this protein NsRpoTp.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Arabidopsis / genetics
  • Base Sequence
  • Bryopsida / metabolism
  • Codon
  • Codon, Initiator
  • DNA, Complementary / metabolism
  • DNA-Directed RNA Polymerases / metabolism*
  • Exons
  • Green Fluorescent Proteins
  • Introns
  • Luminescent Proteins / metabolism
  • Molecular Sequence Data
  • Peptides
  • Phylogeny
  • Plastids / metabolism*
  • Protein Biosynthesis*
  • Protein Structure, Tertiary
  • RNA, Messenger / metabolism*
  • Reverse Transcriptase Polymerase Chain Reaction
  • Sequence Homology, Amino Acid
  • Tobacco / enzymology*


  • Codon
  • Codon, Initiator
  • DNA, Complementary
  • Luminescent Proteins
  • Peptides
  • RNA, Messenger
  • Green Fluorescent Proteins
  • DNA-Directed RNA Polymerases

Associated data

  • GENBANK/AB084950
  • GENBANK/AB084951