HDV ribozyme activity in monovalent cations.
Activity of the two ribozymes from hepatitis delta virus in monovalent salts was examined and compared to activity in Mg2+. Both ribozymes self-cleaved in high concentrations of monovalent cations, and an active site cytosine was required for cleavage activity under those conditions. Cleavage rates were 30-50-fold higher for reactions in LiCl than for reactions in NaCl or NH4Cl, and a thio effect indicated that chemistry was rate-determining for cleavage of the HDV genomic ribozyme in LiCl. Still, in LiCl, there was a more than 100-fold increase in the rate when MgCl2 was included in the reaction. However, the pH-rate profiles for the reactions in LiCl with and without MgCl2 were both bell-shaped with the pH optima in the neutral range. These findings support the idea that monovalent cations can partially substitute for divalent metal ions in the HDV ribozymes, although a divalent metal ion is more effective in supporting catalysis. The absence of a dramatic change in the general shape of pH-rate profiles in LiCl, relative to the profile for reactions including Mg2+, is in contrast to earlier data for the reactions in NaCl and limits our interpretation of the specific role played by the divalent metal ion in the catalytic mechanism.
Perrotta
Anne T
AT
Department of Biochemistry, Box 3711, Duke University Medical Center, Durham, North Carolina 27710, USA.
Been
Michael D
MD
D001483:Base Sequence; D001665:Binding Sites; D002384:Catalysis; D002413:Cations, Divalent / Q000378:metabolism; D002414:Cations, Monovalent / Q000378:metabolism*; D003596:Cytosine / Q000378:metabolism; D016679:Genome, Viral / Q000235:genetics; D003698:Hepatitis Delta Virus / Q000737:chemistry* / Q000201:enzymology*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008274:Magnesium / Q000378:metabolism; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D010710:Phosphates / Q000378:metabolism; D000644:Quaternary Ammonium Compounds / Q000378:metabolism; D016337:RNA, Catalytic / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
D002413:Cations, Divalent; D002414:Cations, Monovalent; D010710:Phosphates; D000644:Quaternary Ammonium Compounds; D016337:RNA, Catalytic; D003596:Cytosine; D008274:Magnesium; C035638:thiophosphoric acid