title: Imidazole rescue of a cytosine mutation in a self-cleaving ribozyme.
abstract: Ribozymes use a number of the same catalytic strategies as protein enzymes. However, general base catalysis by a ribozyme has not been demonstrated. In the hepatitis delta virus antigenomic ribozyme, imidazole buffer rescued activity of a mutant with a cytosine-76 (C76) to uracil substitution. In addition, a C76 to adenine substitution reduced the apparent pKa (where Ka is the acid constant) of the self-cleavage reaction by an amount consistent with differences in the pKa values of these two side chains. These results suggest that, in the wild-type ribozyme, C76 acts as a general base. This finding has implications for potential catalytic functions of conserved cytosines and adenines in other ribozymes and in ribonuclear proteins with enzymatic activity.
authors.affiliation: Department of Biochemistry, Box 3711, Duke University Medical Center, Durham, NC 27710 USA.
authors.forename: A T
authors.initials: AT
authors.lastname: Perrotta
authors.forename: I
authors.initials: I
authors.lastname: Shih
authors.forename: M D
authors.initials: MD
authors.lastname: Been
mesh_terms: D001665:Binding Sites; D002384:Catalysis; D003596:Cytosine / Q000737:chemistry* / Q000378:metabolism / Q000494:pharmacology; D003698:Hepatitis Delta Virus / Q000737:chemistry / Q000201:enzymology*; D006863:Hydrogen-Ion Concentration; D007093:Imidazoles / Q000737:chemistry / Q000378:metabolism* / Q000494:pharmacology; D015636:Magnesium Chloride / Q000494:pharmacology; D008345:Manganese / Q000494:pharmacology; D016296:Mutagenesis; D017354:Point Mutation; D011522:Protons; D011720:Pyrazoles / Q000494:pharmacology; D016337:RNA, Catalytic / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D013696:Temperature
chemical_list: D007093:Imidazoles; D011522:Protons; D011720:Pyrazoles; D016337:RNA, Catalytic; D015636:Magnesium Chloride; C031280:pyrazole; D008345:Manganese; C029899:imidazole; D003596:Cytosine