Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.1.27.4 (ribonuclease)
 6,621 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have used an in vitro system to characterize ribonuclease activities present in spinach chloroplasts. We show that 3' end maturation of petD mRNA, which encodes subunit IV of the cytochrome b6/f complex, is affected by a 33-kDa protein that binds to a hairpin structure at the 3' end of the mature mRNA. Binding of the 33-kDa protein to the petD hairpin structure decreases the efficiency of 3' end maturation, probably by impeding the progress of the processive 3'-5' exonuclease activity involved in chloroplast mRNA processing. A two-base mutation in the stem of the petD hairpin structure creates a novel recognition site for a ribonuclease which competes with the normal processing exonuclease activity. This mutation results in a very low 3' end processing efficiency for mutant petD transcripts, and instead generates a second processing product that lacks a complete hairpin structure. An endonuclease activity which is biochemically distinct from the previously characterized exonuclease activities has also been identified. This endonuclease activity is EDTA-insensitive, and cleaves petD RNA both at the termination codon and at the mature RNA 3' end. Cleavage of petD mRNA at the termination codon leads to rapid degradation of upstream RNA. The possible roles of these ribonuclease activities in chloroplast mRNA decay in vivo are discussed.
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PMID:Specific ribonuclease activities in spinach chloroplasts promote mRNA maturation and degradation. 172 Oct 67

Correct 3' processing of chloroplast precursor mRNAs (pre-mRNAs) requires a stem-loop structure within the 3' untranslated region. In spinach, a stable 3' stem-loop-protein complex has been shown to form in vitro between petD pre-mRNA, encoding subunit IV of the cytochrome b6/f complex, and chloroplast proteins. This complex contains three chloroplast stem-loop binding proteins (CSPs), namely, CSP29, CSP41, and CSP55. Here, we report the purification of CSP41 and cloning of the csp41 gene and show that CSP41 is encoded by a single nuclear gene. Characterization of bacterially expressed CSP41 demonstrates that this protein binds specifically to the 3' stem-loop structure and a downstream AU-rich element of petD pre-mRNA and that its binding affinity is enhanced by associating with CSP55. Our data also show that CSP41 has substantial nonspecific endoribonuclease activity. These data suggest that CSP41 could be involved in 3' processing of petD pre-mRNA and/or in RNA degradation. The fact that different reaction conditions favor RNA binding over ribonuclease activities suggests a possible mode of in vivo regulation.
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PMID:CSP41, a sequence-specific chloroplast mRNA binding protein, is an endoribonuclease. 877 2

Spinach CSP41 is part of a protein complex that binds to the 3' untranslated region (UTR) of petD precursor-mRNA, a chloroplast gene encoding subunit IV of the cytochrome b6/f complex. CSP41 cleaves the 3'-UTR of petD mRNA within the stem-loop structure, suggesting a key role in the control of chloroplast mRNA stability. We discovered that CSP41 is homologous to nucleotide-sugar epimerases and hydroxysteroid dehydrogenases while seeking distant homologs of these enzymes with a hidden Markov model-based search of Genpept. This analysis identified Synechocystis ORF, Accession 1652543 as a homolog. Subsequent analyses show that spinach CSP41 and Arabidopsis thaliana 2765081 are homologous to the Synechocystis ORF. Information from the solved 3D structures of epimerases and dehydrogenases and our motif analysis of these enzymes is used to predict domains on CSP41 that are important in binding and metabolism of mRNA. Cyanobacteria are among the earliest life forms, indicating that the divergence from a common ancestor of nucleotide-sugar epimerases and an mRNA binding protein with ribonuclease activity was ancient.
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PMID:Spinach CSP41, an mRNA-binding protein and ribonuclease, is homologous to nucleotide-sugar epimerases and hydroxysteroid dehydrogenases. 967 22