title: A role for initiation codon context in chloroplast translation.
abstract: To study the role of initiation codon context in chloroplast protein synthesis, we mutated the three nucleotides immediately upstream of the initiation codon (the -1 triplet) of two chloroplast genes in the alga Chlamydomonas reinhardtii. In prokaryotes, the -1 triplet has been proposed to base pair with either the 530 loop of 16S rRNA or the extended anticodon of fMet-tRNA. We found that in vivo, none of the chloroplast mutations affected mRNA stability. However, certain mutations did cause a temperature-sensitive decrease in translation and a more dramatic decrease at room temperature when combined with an AUU initiation codon. These mutations disrupt the proposed extended base pairing interaction with the fMet-tRNA anticodon loop, suggesting that this interaction may be important in vivo. Mutations that would still permit base pairing with the 530 loop of the 16S rRNA also had a negative effect on translation, suggesting that this interaction does not occur in vivo. Extended base pairing surrounding the initiation codon may be part of a mechanism to compensate for the lack of a classic Shine-Dalgarno rRNA interaction in the translation of some chloroplast mRNAs.
authors.affiliation: Department of Molecular Biology and Genetics and Boyce Thompson Institute for Plant Research, Cornell University, Tower Road, Ithaca, New York 14853, USA.
authors.forename: D
authors.initials: D
authors.lastname: Esposito
authors.forename: A J
authors.initials: AJ
authors.lastname: Hicks
authors.forename: D B
authors.initials: DB
authors.lastname: Stern
mesh_terms: D000818:Animals; D001483:Base Sequence; D016825:Chlamydomonas reinhardtii / Q000235:genetics*; D002736:Chloroplasts / Q000235:genetics*; D003062:Codon / Q000235:genetics*; D008969:Molecular Sequence Data; D009154:Mutation; D010442:Peptide Chain Initiation, Translational; D010940:Plant Proteins / Q000235:genetics; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000235:genetics; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D014170:Transformation, Genetic
chemical_list: D003062:Codon; D010940:Plant Proteins; D012333:RNA, Messenger; D012336:RNA, Ribosomal, 16S