Structure of the chloroplast ribosome: novel domains for translation regulation.
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 A. 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.
Department of Cell Biology, The Scripps Research Institute, La Jolla, California, United States of America.
Andrea L
AL
Manuell
Joel
J
Quispe
Stephen P
SP
Mayfield
D020121:5' Untranslated Regions; D020418:Algal Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D016825:Chlamydomonas reinhardtii / Q000737:chemistry / Q000235:genetics; D002736:Chloroplasts / Q000737:chemistry / Q000235:genetics / Q000378:metabolism / Q000648:ultrastructure; D020285:Cryoelectron Microscopy; D018506:Gene Expression Regulation, Plant; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D014176:Protein Biosynthesis; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D021122:Protein Subunits / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000737:chemistry / Q000378:metabolism; D012270:Ribosomes / Q000235:genetics / Q000378:metabolism / Q000648:ultrastructure*
D020121:5' Untranslated Regions; D020418:Algal Proteins; D001426:Bacterial Proteins; D021122:Protein Subunits; D012333:RNA, Messenger