Open AccessTermination codon-dependent translation of partially overlapping ndhC-ndhK transcripts in chloroplasts
Author(s) -
Maki Yukawa,
Masahiro Sugiura
Publication year - 2008
Publication title -
proceedings of the national academy of sciences of the united states of america
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.011
H-Index - 771
eISSN - 1091-6490
pISSN - 0027-8424
DOI - 10.1073/pnas.0809240105
Subject(s) - cistron , stop codon , frameshift mutation , biology , five prime untranslated region , start codon , genetics , translation (biology) , eukaryotic translation , translational efficiency , messenger rna , chloroplast , microbiology and biotechnology , gene , rna , mutation
The chloroplast NAD(P)H dehydrogenase complex, a homologue of mitochondrial complex I, consists of >15 subunits, of which 11 are encoded by the chloroplast genome (ndhA-K ). ThendhC andndhK genes are partially overlapped and cotranscribed in many land plants. The downstreamndhK mRNA possesses 4 possible AUG initiation codons in many dicot plants. By using an efficient in vitro translation system from tobacco chloroplasts, we defined that the major initiation site of tobaccondhK mRNAs is the third AUG that is located 4 nt upstream from thendhC stop codon. Mutation of thendhC stop codon (UAG) arrested translation of thendhK cistron. Frameshift of thendhC coding strand inhibited also translation of the distal cistron. The results indicated thatndhK translation depends on termination of the preceding cistron, namely translational coupling. Surprisingly, removal of thendhC 5′-UTR and its AUG still supported substantial translation of thendhK cistron. This translation was abolished again by removing thendhC stop codon. Although translation of the downstream cistron of an overlapping mRNA is generally very low, we found that thendhC /K mRNA produces NdhK and NdhC in similar amounts. Based on subunit compositions of the bacterial complex I, the stoichiometry of NdhK and NdhC is suggested to be 1:1 in chloroplasts. To meet this stoichiometry, thendhC /K mRNA is translated not only by a translational coupling event but also by a termination codon-dependent pathway.