Non-AUG translation initiation of mRNA encoding plastid-targeted phage-type RNA polymerase in Nicotiana sylvestris.
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.
Kobayashi
Yuki
Y
Center for Gene Research, Nagoya University, Chikusa, 464-8602, Nagoya, Japan.
Dokiya
Yuko
Y
Kumazawa
Yoshinori
Y
Sugita
Mamoru
M
D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics; D001483:Base Sequence; D019068:Bryopsida / Q000378:metabolism; D003062:Codon; D018387:Codon, Initiator; D018076:DNA, Complementary / Q000378:metabolism; D012321:DNA-Directed RNA Polymerases / Q000378:metabolism*; D005091:Exons; D049452:Green Fluorescent Proteins; D007438:Introns; D008164:Luminescent Proteins / Q000378:metabolism; D008969:Molecular Sequence Data; D010455:Peptides; D010802:Phylogeny; D018087:Plastids / Q000378:metabolism*; D014176:Protein Biosynthesis; D017434:Protein Structure, Tertiary; D012333:RNA, Messenger / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid; D014026:Nicotiana / Q000201:enzymology*
D003062:Codon; D018387:Codon, Initiator; D018076:DNA, Complementary; D008164:Luminescent Proteins; D010455:Peptides; D012333:RNA, Messenger; D049452:Green Fluorescent Proteins; D012321:DNA-Directed RNA Polymerases