title: Processing of the psbA 5' untranslated region in Chlamydomonas reinhardtii depends upon factors mediating ribosome association.
abstract: The 5' untranslated region of the chloroplast psbA mRNA, encoding the D1 protein, is processed in Chlamydomonas reinhardtii. Processing occurs just upstream of a consensus Shine-Dalgarno sequence and results in the removal of 54 nucleotides from the 5' terminus, including a stem-loop element identified previously as an important structure for D1 expression. Examination of this processing event in C. reinhardtii strains containing mutations within the chloroplast or nuclear genomes that block psbA translation reveals a correlation between processing and ribosome association. Mutations within the 5' untranslated region of the psbA mRNA that disrupt the Shine-Dalgarno sequence, acting as a ribosome binding site, preclude translation and prevent mRNA processing. Similarly, nuclear mutations that specifically affect synthesis of the D1 protein specifically affect processing of the psbA mRNA. In vitro, loss of the stem-loop element does not prohibit the binding of a message-specific protein complex required for translational activation of psbA upon illumination. These results are consistent with a hierarchical maturation pathway for chloroplast messages, mediated by nuclear-encoded factors, that integrates mRNA processing, message stability, ribosome association, and translation.
authors.affiliation: Department of Cell Biology and The Skaggs Institute for Chemical Biology, The Scripps Research Institute, La Jolla, California 92037, USA.
authors.forename: R K
authors.initials: RK
authors.lastname: Bruick
authors.forename: S P
authors.initials: SP
authors.lastname: Mayfield
mesh_terms: D020121:5' Untranslated Regions / Q000235:genetics* / Q000378:metabolism*; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D002467:Cell Nucleus / Q000235:genetics / Q000378:metabolism; D016825:Chlamydomonas reinhardtii / Q000235:genetics* / Q000378:metabolism* / Q000528:radiation effects; D002736:Chloroplasts / Q000235:genetics / Q000378:metabolism; D017931:DNA Primers / Q000235:genetics; D008027:Light; D008969:Molecular Sequence Data; D009154:Mutation; D009690:Nucleic Acid Conformation; D045322:Photosynthetic Reaction Center Complex Proteins / Q000235:genetics* / Q000378:metabolism / Q000528:radiation effects; D045332:Photosystem II Protein Complex; D012323:RNA Processing, Post-Transcriptional; D012333:RNA, Messenger / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D018749:RNA, Plant / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D016053:RNA, Protozoan / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012270:Ribosomes / Q000378:metabolism
chemical_list: D020121:5' Untranslated Regions; D017931:DNA Primers; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D012333:RNA, Messenger; D018749:RNA, Plant; D016053:RNA, Protozoan