Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.1.26.4 (RNase H)
 2,751 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Both prokaryotic and eukaryotic cells contain multiple forms of ribonuclease H, a ribonuclease that specifically degrades the RNA strand of RNA-DNA hybrids and which has been implicated in the processing of initiator RNAs and in the removal of RNA primers from Okazaki fragments. The Crithidia fasciculata RNH1 gene encodes an RNase H and was shown to be a single-copy gene in this diploid trypanosomatid. The RNH1 gene has been disrupted by targeted gene disruption using hygromycin or G418 drug-resistance cassettes. Major active forms of RNase H (38 and 45 kDa) were observed on activity gels of extracts of wild-type cells or cells in which one allele of RNH1 was disrupted. Both the 38 and 45 kDa activities were absent in extracts of cells in which both alleles of RNH1 were disrupted indicating that both forms of the C.fasciculata RNase H are encoded by the RNH1 gene.
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PMID:Disruption of the Crithidia fasciculata RNH1 gene results in the loss of two active forms of ribonuclease H. 763 Jul 31

A gene designated Cfa RNH1 has been cloned by complementation of an RNase H deficiency in an Escherichia coli rnhA mutant by using a genomic DNA library from the trypanosomatid Crithidia fasciculata. The encoded RNase H is predicted to have 494 amino acid residues and a molecular mass of 53.7 kDa. The carboxyl half of the protein is homologous to the 155-residue E. coli RNase HI (41% identity) and the 166-residue Saccharomyces cerevisiae RNase HI (33% identity). The recombinant protein has been purified as a six-histidine-tagged fusion protein by metal chelate chromatography and was shown to have RNase H activity. Antibodies against the recombinant protein recognize proteins of approximately 65 kDa and 56 kDa on Western blots of C. fasciculata extracts. These results demonstrate the feasibility of cloning trypanosome genes by complementation of appropriate E. coli mutants with genomic DNA libraries.
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PMID:Functional complementation of an Escherichia coli ribonuclease H mutation by a cloned genomic fragment from the trypanosomatid Crithidia fasciculata. 841 5

The Crithidia fasciculata RNH1 gene encodes an RNase H, an enzyme that specifically degrades the RNA strand of RNA-DNA hybrids. The RNH1 gene is contained within an open reading frame (ORF) predicted to encode a protein of 53.7 kDa. Previous work has shown that RNH1 expresses two proteins: a 38 kDa protein and a 45 kDa protein which is enriched in kinetoplast extracts. Epitope tagging of the C-terminus of the RNH1 gene results in localization of the protein to both the kinetoplast and the nucleus. Translation of the ORF beginning at the second in-frame methionine codon predicts a protein of 38 kDa. Insertion of two tandem stop codons between the first ATG codon and the second in-frame ATG codon of the ORF results in expression of only the 38 kDa protein and the protein localizes specifically to the nucleus. Mutation of the second methionine codon to a valine codon prevents expression of the 38 kDa protein and results in exclusive production of the 45 kDa protein and localization of the protein only in the kinetoplast. These results suggest that the kinetoplast enzyme results from processing of the full-length 53.7 kDa protein. The nuclear enzyme appears to result from translation initiation at the second in-frame ATG codon. This is the first example in trypanosomatids of the production of nuclear and mitochondrial isoforms of a protein from a single gene and is the only eukaryotic gene in the RNase HI gene family shown to encode a mitochondrial RNase H.
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PMID:The Crithidia fasciculata RNH1 gene encodes both nuclear and mitochondrial isoforms of RNase H. 1116 Aug 95

RNase H1 from extreme halophilic archaeon Halobacterium sp. NRC-1 (Halo-RNH1) consists of an N-terminal domain with unknown function and a C-terminal RNase H domain. It is characterized by the high content of acidic residues on the protein surface. The far- and near-UV CD spectra of Halo-RNH1 suggested that Halo-RNH1 assumes a partially folded structure in the absence of salt and divalent metal ions. It requires either salt or divalent metal ions for folding. However, thermal denaturation of Halo-RNH1 analyzed in the presence of salt and/or divalent metal ions by CD spectroscopy suggested that salt and divalent metal ions independently stabilize the protein and thereby facilitate folding. Divalent metal ions stabilize the protein probably by binding mainly to the active site and suppressing negative charge repulsions at this site. Salt stabilizes the protein probably by increasing hydrophobic interactions at the protein core and decreasing negative charge repulsions on the protein surface. Halo-RNH1 exhibited activity in the presence of divalent metal ions regardless of the presence or absence of 3 M NaCl. However, higher concentrations of divalent metal ions are required for activity in the absence of salt to facilitate folding. Thus, divalent metal ions play a dual role in catalysis and folding of Halo-RNH1. Construction of the Halo-RNH1 derivatives lacking an N- or C-terminal domain, followed by biochemical characterizations, indicated that an N-terminal domain is dispensable for stability, activity, folding, and substrate binding of Halo-RNH1.
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PMID:A dual role of divalent metal ions in catalysis and folding of RNase H1 from extreme halophilic archaeon Halobacterium sp. NRC-1. 2377 68