Abstract
Gene expression in chloroplasts is controlled primarily through the regulation of translation. This regulation allows coordinate expression between the plastid and nuclear genomes, and is responsive to environmental conditions. Despite common ancestry with bacterial translation, chloroplast translation is more complex and involves positive regulatory mRNA elements and a host of requisite protein translation factors that do not have counterparts in bacteria. Previous proteomic analyses of the chloroplast ribosome identified a significant number of chloroplast-unique ribosomal proteins that expand upon a basic bacterial 70S-like composition. In this study, cryo-electron microscopy and single-particle reconstruction were used to calculate the structure of the chloroplast ribosome to a resolution of 15.5 Å. Chloroplast-unique proteins are visualized as novel structural additions to a basic bacterial ribosome core. These structures are located at optimal positions on the chloroplast ribosome for interaction with mRNAs during translation initiation. Visualization of these chloroplast-unique structures on the ribosome, combined with mRNA cross-linking, allows us to propose a model for translation initiation in chloroplasts in which chloroplast-unique ribosomal proteins interact with plastid-specific translation factors and RNA elements to facilitate regulated translation of chloroplast mRNAs.
Highlights
The chloroplast of plants and algae is believed to have originated from the endosymbiosis of an ancient photosynthetic bacteria into a eukaryotic host
Translation of many chloroplast genes is regulated in response to light, and to maintain stoichiometric accumulation of multiprotein-complex subunits [7,8]. All of this regulation involves a host of protein translation factors, and the formation of RNA–protein complexes on chloroplast mRNA 59 untranslated regions (59 UTRs) [9,10,11,12,13]
We present the three-dimensional structure of the chloroplast ribosome, as calculated using cryo-electron microscopy and single-particle reconstruction
Summary
The chloroplast of plants and algae is believed to have originated from the endosymbiosis of an ancient photosynthetic bacteria into a eukaryotic host. Translation of many chloroplast genes is regulated in response to light, and to maintain stoichiometric accumulation of multiprotein-complex subunits [7,8]. All of this regulation involves a host of protein translation factors, and the formation of RNA–protein complexes on chloroplast mRNA 59 untranslated regions (59 UTRs) [9,10,11,12,13]. Some of these protein factors are specific to individual mRNAs, whereas others serve classes of messages
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
