A role for initiation codon context in chloroplast translation |
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Authors: | Esposito D Hicks A J Stern D B |
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Affiliation: | Department of Molecular Biology and Genetics and Boyce Thompson Institute for Plant Research, Cornell University, Tower Road, Ithaca, New York 14853, USA. |
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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. |
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