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Query: EC:1.6.99.3 (diaphorase)
 5,903 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Tobacco chloroplast genes encoding a photosystem I component (psaC) and a NADH dehydrogenase subunit (ndhD) are transcribed as a dicistronic pre-mRNA which is then cleaved into short mRNAs. An RNA protection assay revealed that the cleavage occurs at multiple sites in the intercistronic region. There are two possible initiation codons in the tobacco ndhD mRNA: the upstream AUG and the AUG created by RNA editing from the in-frame ACG located 25 nt downstream. Using the chloroplast in vitro translation system, we found that translation begins only from the edited AUG. The extent of ACG to AUG editing is partial and depends on developmental and environmental conditions. In addition, the in vitro assay showed that the psaC/ndhD dicistronic mRNA is not functional and that the intercistronic cleavage is a prerequisite for both ndhD and psaC translation. Using a series of mutant mRNAs, we showed that an intramolecular interaction between an 8 nt sequence in the psaC coding region and its complementary 8 nt sequence in the 5' ndhD UTR is the negative element for translation of the dicistronic mRNA. A possible mechanism in which the differential expression of the chloroplast operon consists of functionally unrelated genes is discussed.
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PMID:Both RNA editing and RNA cleavage are required for translation of tobacco chloroplast ndhD mRNA: a possible regulatory mechanism for the expression of a chloroplast operon consisting of functionally unrelated genes. 936 94

Gene expression in chloroplasts is strongly regulated at the post-transcriptional level. Most post-transcriptional mechanisms require RNA-protein complexes. Here we report an analysis of RNA-protein complexes that form in the 5' untranslated regions (5'UTRs) of spinach chloroplast mRNAs. Previous studies from our laboratory showed that four ATP synthase 5'UTRs were able to compete with each other for binding by proteins in a chloroplast extract. This implied that at least some of the binding proteins recognized all four of those ATP synthase 5'UTRs. Here, we examine whether the binding proteins are ATP synthase-specific by performing competition-binding assays between an ATP synthase 5'UTR and 5'UTRs from other chloroplast genes. Competition substrates were chosen to represent a wide range of chloroplast mRNAs, including those encoding the photosystems, NADH dehydrogenase, cytochromes and ribosomal subunits, and two previously unexamined ATP synthase subunits. Results from these experiments revealed that, although the ATP synthase-binding proteins do not bind universally to every chloroplast 5'UTR, they do bind to the majority (12/14) of those examined. Thus, these RNA-binding proteins are candidates for factors that link the post-transcriptional expression of many chloroplast genes of disparate function.
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PMID:Proteins are shared among RNA-protein complexes that form in the 5' untranslated regions of spinach chloroplast mRNAs. 1207 1

The mitochondrial rotenone-sensitive NADH:ubiquinone oxidoreductase (complex I) comprises more than 35 subunits, the majority of which are encoded by the nucleus. In Chlamydomonas reinhardtii, only five components (ND1, ND2, ND4, ND5 and ND6) are coded for by the mitochondrial genome. Here, we characterize two mitochondrial mutants (dum5 and dum17) showing strong reduction or inactivation of complex I activity: dum5 is a 1T deletion in the 3' UTR of nd5 whereas dum17 is a 1T deletion in the coding sequence of nd6. The impact of these mutations and of mutations affecting nd1, nd4 and nd4/nd5 genes on the assembly of complex I is investigated. After separation of the respiratory complexes by blue native (BN)-PAGE or sucrose gradient centrifugation, we demonstrate that the absence of intact ND1 or ND6 subunit prevents the assembly of the 850 kDa whole complex, whereas the loss of ND4 or ND4/ND5 leads to the formation of a subcomplex of 650 kDa present in reduced amount. The implications of our findings for the possible role of these ND subunits on the activity of complex I and for the structural organization of the membrane arm of the enzyme are discussed. In mitochondria from all the strains analyzed, we moreover detected a 160-210 kDa fragment comprising the hydrophilic 49 kDa and 76 kDa subunits of the complex I peripheral arm and showing NADH dehydrogenase activity.
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PMID:Impact of mutations affecting ND mitochondria-encoded subunits on the activity and assembly of complex I in Chlamydomonas. Implication for the structural organization of the enzyme. 1207 58