Publications

• Expression and regulation by interferon of a double-stranded-RNA-specific adenosine deaminase from human cells: evidence for two forms of the deaminase.

  Patterson J.B., Samuel C.E.

  A 6,474-nucleotide human cDNA clone designated K88, which encodes double-stranded RNA (dsRNA)-specific adenosine deaminase, was isolated in a screen for interferon (IFN)-regulated cDNAs. Northern (RNA) blot analysis revealed that the K88 cDNA hybridized to a single major transcript of approximatel ... >> More

  A 6,474-nucleotide human cDNA clone designated K88, which encodes double-stranded RNA (dsRNA)-specific adenosine deaminase, was isolated in a screen for interferon (IFN)-regulated cDNAs. Northern (RNA) blot analysis revealed that the K88 cDNA hybridized to a single major transcript of approximately 6.7 kb in human cells which was increased about fivefold by IFN treatment. Polyclonal antisera prepared against K88 cDNA products expressed in Escherichia coli as glutathione S-transferase (GST) fusion proteins recognized two proteins by Western (immunoblot) analysis. An IFN-induced 150-kDa protein and a constitutively expressed 110-kDa protein whose level was not altered by IFN treatment were detected in human amnion U and neuroblastoma SH-SY5Y cell lines. Only the 150-kDa protein was detected in mouse fibroblasts with antiserum raised against the recombinant human protein; the mouse 150-kDa protein was IFN inducible. Immunofluorescence microscopy and cell fractionation analyses showed that the 110-kDa protein was exclusively nuclear, whereas the 150-kDa protein was present in both the cytoplasm and nucleus of human cells. The amino acid sequence deduced from the K88 cDNA includes three copies of the highly conserved R motif commonly found in dsRNA-binding proteins. Both the 150-kDa and the 110-kDa proteins prepared from human nuclear extracts bound to double-stranded but not to single-stranded RNA affinity columns. Furthermore, E. coli-expressed GST-K88 fusion proteins that included the R motif possessed dsRNA-binding activity. Extracts prepared either from K88 cDNA-transfected cells or from IFN-treated cells contained increased dsRNA-specific adenosine deaminase enzyme activity. These results establish that K88 encodes an IFN-inducible dsRNA-specific adenosine deaminase and suggest that at least two forms of dsRNA-specific adenosine deaminase occur in human cells. << Less

  Mol. Cell. Biol. 15:5376-5388(1995) [PubMed] [EuropePMC]

• Purification of native and recombinant double-stranded RNA-specific adenosine deaminases.

  O'Connell M.A., Gerber A., Keegan L.P.

  ADAR1 and ADAR2 are members of a family of enzymes that catalyze the conversion of adenosine to inosine in double-stranded RNA. Unlike the other types of RNA editing that involve multiprotein editing complexes, the site-specific deamination of an adenosine to inosine is catalyzed by single enzymes ... >> More

  ADAR1 and ADAR2 are members of a family of enzymes that catalyze the conversion of adenosine to inosine in double-stranded RNA. Unlike the other types of RNA editing that involve multiprotein editing complexes, the site-specific deamination of an adenosine to inosine is catalyzed by single enzymes. ADAR1 and ADAR2 have been purified and the genes cloned from various sources. Each gene encodes multiple splice variants. As it is crucial to have an adequate supply of pure protein to investigate this type of RNA editing, we describe in this article methods for both the purification and the overexpression of either full-length or partial ADAR1 and ADAR2 isoforms. << Less

  Methods 15:51-62(1998) [PubMed] [EuropePMC]

• Two forms of human double-stranded RNA-specific editase 1 (hRED1) generated by the insertion of an Alu cassette.

  Gerber A., O'Connell M.A., Keller W.

  The double-stranded RNA-specific editase 1 (RED1/ADAR2) is implicated in the editing of precursor-mRNAs (pre-mRNA) encoding subunits of glutamate receptors (GluRs) in brain. Site-specific deamination of adenosine to inosine alters the codon at the Q/R site in GluR-B rendering the heteromeric recep ... >> More

  The double-stranded RNA-specific editase 1 (RED1/ADAR2) is implicated in the editing of precursor-mRNAs (pre-mRNA) encoding subunits of glutamate receptors (GluRs) in brain. Site-specific deamination of adenosine to inosine alters the codon at the Q/R site in GluR-B rendering the heteromeric receptor impermeable to Ca2+ ions. We cloned human RED1 (hRED1/hADAR2) cDNAs from a brain cDNA library. The human enzyme is 95% identical to the rat homologue. We characterized two alternatively spliced forms that differed by the presence of an Alu-J cassette in the deaminase domain. For the long form containing the Alu cassette, we isolated cDNA clones with an alternative C-terminus and 3'-UTR. An 8.8-kb transcript of hRED1 is most abundant in brain and heart, and lower levels are detected in other tissues. In vitro editing assays with purified recombinant hRED1 containing or lacking the Alu-J cassette revealed that both forms of the protein have the same substrate specificity, but differ in their catalytic activity. << Less

  RNA 3:453-463(1997) [PubMed] [EuropePMC]

• Inositol hexakisphosphate is bound in the ADAR2 core and required for RNA editing.

  Macbeth M.R., Schubert H.L., Vandemark A.P., Lingam A.T., Hill C.P., Bass B.L.

  We report the crystal structure of the catalytic domain of human ADAR2, an RNA editing enzyme, at 1.7 angstrom resolution. The structure reveals a zinc ion in the active site and suggests how the substrate adenosine is recognized. Unexpectedly, inositol hexakisphosphate (IP6) is buried within the ... >> More

  We report the crystal structure of the catalytic domain of human ADAR2, an RNA editing enzyme, at 1.7 angstrom resolution. The structure reveals a zinc ion in the active site and suggests how the substrate adenosine is recognized. Unexpectedly, inositol hexakisphosphate (IP6) is buried within the enzyme core, contributing to the protein fold. Although there are no reports that adenosine deaminases that act on RNA (ADARs) require a cofactor, we show that IP6 is required for activity. Amino acids that coordinate IP6 in the crystal structure are conserved in some adenosine deaminases that act on transfer RNA (tRNA) (ADATs), related enzymes that edit tRNA. Indeed, IP6 is also essential for in vivo and in vitro deamination of adenosine 37 of tRNAala by ADAT1. << Less

  Science 309:1534-1539(2005) [PubMed] [EuropePMC]

• Purification of the Xenopus laevis double-stranded RNA adenosine deaminase.

  Hough R.F., Bass B.L.

  A double-stranded RNA adenosine deaminase that catalyzes the conversion of adenosines to inosines in duplex RNA substrates was purified to near homogeneity from Xenopus laevis eggs. The final specific activity was approximately 2.0 nmol of inosine min-1 mg-1 at 25 degrees C and pH 7.9 with a 794-b ... >> More

  A double-stranded RNA adenosine deaminase that catalyzes the conversion of adenosines to inosines in duplex RNA substrates was purified to near homogeneity from Xenopus laevis eggs. The final specific activity was approximately 2.0 nmol of inosine min-1 mg-1 at 25 degrees C and pH 7.9 with a 794-base pair RNA substrate. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed a single major approximately 120-kDa protein band by silver staining. The purified enzyme migrated with an apparent molecular mass of 90 +/-10 kDa during high performance liquid chromatography. Gel filtration of the partially purified enzyme gave an apparent molecular mass of 210 +/-20 kDa, suggesting that the enzyme may dimerize or associate with other cellular components. Substrate modification was inhibited by excess substrate, thiol reagents, heparin, and moderate concentrations of monovalent cations. << Less

  J Biol Chem 269:9933-9939(1994) [PubMed] [EuropePMC]

• Substrate recognition by ADAR1 and ADAR2.

  Wong S.K., Sato S., Lazinski D.W.

  RNA editing catalyzed by ADAR1 and ADAR2 involves the site-specific conversion of adenosine to inosine within imperfectly duplexed RNA. ADAR1- and ADAR2-mediated editing occurs within transcripts of glutamate receptors (GluR) in the brain and in hepatitis delta virus (HDV) RNA in the liver. Althou ... >> More

  RNA editing catalyzed by ADAR1 and ADAR2 involves the site-specific conversion of adenosine to inosine within imperfectly duplexed RNA. ADAR1- and ADAR2-mediated editing occurs within transcripts of glutamate receptors (GluR) in the brain and in hepatitis delta virus (HDV) RNA in the liver. Although the Q/R site within the GluR-B premessage is edited more efficiently by ADAR2 than it is by ADAR1, the converse is true for the +60 site within this same transcript. ADAR1 and ADAR2 are homologs having two common functional regions, an N-terminal double-stranded RNA-binding domain and a C-terminal deaminase domain. It is neither understood why only certain adenosines within a substrate molecule serve as targets for ADARs, nor is it known which domain of an ADAR confers its specificity for particular editing sites. To assess the importance of several aspects of RNA sequence and structure on editing, we evaluated 20 different mutated substrates, derived from four editing sites, for their ability to be edited by either ADAR1 or ADAR2. We found that when these derivatives contained an A:C mismatch at the editing site, editing by both ADARs was enhanced compared to when A:A or A:G mismatches or A:U base pairs occurred at the same site. Hence substrate recognition and/or catalysis by ADARs could involve the base that opposes the edited adenosine. In addition, by using protein chimeras in which the deaminase domains were exchanged between ADAR1 and ADAR2, we found that this domain played a dominant role in defining the substrate specificity of the resulting enzyme. << Less

  RNA 7:846-858(2001) [PubMed] [EuropePMC]

• Molecular cloning of cDNA for double-stranded RNA adenosine deaminase, a candidate enzyme for nuclear RNA editing.

  Kim U., Wang Y., Sanford T., Zeng Y., Nishikura K.

  We have cloned human cDNA encoding double-stranded RNA adenosine deaminase (DRADA). DRADA is a ubiquitous nuclear enzyme that converts multiple adenosines to inosines in double-helical RNA substrates without apparent sequence specificity. The A --> I conversion activity of the protein encoded by t ... >> More

  We have cloned human cDNA encoding double-stranded RNA adenosine deaminase (DRADA). DRADA is a ubiquitous nuclear enzyme that converts multiple adenosines to inosines in double-helical RNA substrates without apparent sequence specificity. The A --> I conversion activity of the protein encoded by the cloned cDNA was confirmed by recombinant expression in insect cells. Use of the cloned DNA as a molecular probe documented sequence conservation across mammals and detected a single transcript of 7 kb in RNA of all human tissues analyzed. The deduced primary structure of human DRADA revealed a bipartite nuclear localization signal, three repeats of a double-stranded RNA binding motif, and the presence of sequences conserved in the catalytic center of other deaminases, including a cytidine deaminase involved in the RNA editing of apolipoprotein B. These structural properties are consistent with the enzymatic signature of DRADA, and strengthen the hypothesis that DRADA carries out the RNA editing of transcripts encoding glutamate-gated ion channels in brain. << Less

  Proc. Natl. Acad. Sci. U.S.A. 91:11457-11461(1994) [PubMed] [EuropePMC]

• Requirement of dimerization for RNA editing activity of adenosine deaminases acting on RNA.

  Cho D.-S.C., Yang W., Lee J.T., Shiekhattar R., Murray J.M., Nishikura K.

  Adenosine deaminases acting on RNA (ADAR) convert adenosine residues into inosines in double-stranded RNA. Three vertebrate ADAR gene family members, ADAR1, ADAR2, and ADAR3, have been identified. The catalytic domain of all three ADAR gene family members is very similar to that of Escherichia col ... >> More

  Adenosine deaminases acting on RNA (ADAR) convert adenosine residues into inosines in double-stranded RNA. Three vertebrate ADAR gene family members, ADAR1, ADAR2, and ADAR3, have been identified. The catalytic domain of all three ADAR gene family members is very similar to that of Escherichia coli cytidine deaminase and APOBEC-1. Homodimerization is essential for the enzyme activity of those cytidine deaminases. In this study, we investigated the formation of complexes between differentially epitope-tagged ADAR monomers by sequential affinity chromatography and size exclusion column chromatography. Both ADAR1 and ADAR2 form a stable enzymatically active homodimer complex, whereas ADAR3 remains as a monomeric, enzymatically inactive form. No heterodimer complex formation among different ADAR gene family members was detected. Analysis of HeLa and mouse brain nuclear extracts suggested that endogenous ADAR1 and ADAR2 both form a homodimer complex. Interestingly, endogenous ADAR3 also appears to form a homodimer complex, indicating the presence of a brain-specific mechanism for ADAR3 dimerization. Homodimer formation may be necessary for ADAR to act as active deaminases. Analysis of dimer complexes consisting of one wild-type and one mutant monomer suggests functional interactions between the two subunits during site-selective RNA editing. << Less

  J. Biol. Chem. 278:17093-17102(2003) [PubMed] [EuropePMC]