PDribofuranosyl1 2 4triazole3carboxamide See ribavirin

ribonuclease A The principal active component of bovine pancreatic ribonuclease; cleaves phosphodiester bonds between pyrimidines and adjacent nucleotides. Pure purine polymers are relatively resistant to attack by RNase A, but sufficiently high enzyme concentrations will degrade poly A, for example.

ribonuclease B A component of bovine pancreatic ribonuclease which can be separated from ribonuclease A by ionexchange chromatography, and is present in ten-fold lower concentration.

ribonuclease C Isolated from human placenta. Preferentially cleaves RNA on the 5' side of cytidine residues.

ribonuclease D A ribonuclease that removes nucleotides from precursor tRNA molecules, generating the 3' terminus of mature tRNA.

ribonuclease from Bacillus cereus A ribonuclease which cleaves the 3'-phosphodiester bonds after pyrimidine residues.

ribonuclease H A ribonuclease which specifically cleaves the RNA strand present in an RNA-DNA hybrid, but does not digest free single-stranded or double-stranded RNA. Can be isolated from Escherichia coli; also present as part of the reverse transcriptase activity of retroviruses. Used experimentally to remove poly A tails from mRNA after hybridization with poly dT.

Oberhaus SM and Newbold JE (1995) J Virol 69, 5697

ribonuclease III A ribonuclease that hydrolyzes double-stranded RNA. An endoribonuclease from Escherichia coli which cleaves double-stranded RNA to single-stranded RNA of approximately 15 nt chain length. The enzyme also cleaves specific sequences in single-stranded RNA, and is responsible for processing large RNA transcripts of bacteriophage T7 DNA into individual early mRNAs.

Dunn JJ (1975) J Biol Chem 251, 3807

ribonuclease P A processing enzyme, involved in tRNA biosynthesis in Escherichia coli, which cleaves tRNA precursor molecules, removing 5' proximal nucleotides to generate the 5' termini of mature tRNA molecules.

ribonuclease Phy 1 A ribonuclease isolated from a slime mold, Physarum poly-cephalum. Preferentially cleaves the phosphodiester bonds between guanine, adenine and uracil and adjacent residues. Used in RNA sequence analysis to discriminate between cytosine and uracil.

Simoncsits A et al (1977) Nature 269, 833

ribonuclease Phy M A ribonuclease that cleaves on the 3' side of adenine and uri-dine residues.

ribonuclease S A preparation of ribo-nuclease A in which the main peptide chain has been cleaved with subtilisin (proteinase from Bacillus subtilis). The enzyme activity of RNase S is very similar to that of RNase A.

ribonuclease T1 A ribonuclease isolated from taka-diastase which cleaves phos-phodiester bonds between 3' guanylic acid groups and the 5' hydroxyl groups of adjacent nucleotides. It has also been termed 'guanyloribonuclease'.

ribonuclease T2 A ribonuclease isolated from taka-diastase which cleaves phos-phodiester bonds between any pair of ribonuclease T2

nucleotides, but displays a preference for adenylic acid bonds.

ribonuclease U2 A ribonuclease found in culture broth of the smut fungus, Ustilago sphaerogena, which cleaves an RNA molecule at the phosphodiester bonds of purine nucleotides to yield 3' nucleotides with intermediary formation of purine nucleoside 2'-3' cyclic phosphates.

ribonucleic acid (RNA) A polymer of ribonucleotides which differs in several respects from DNA. Three of the bases, adenine, guanine and cytosine, are the same as in DNA but uracil replaces thymine and a few minor or modified bases are present, especially in tRNA. The d-ribose sugar of RNA differs from the 2-deoxy-d-ribose of DNA in having four rather than three hydroxyl groups. Complementarity of the bases seen in DNA is not evident. Thus long double strands are not formed but short stretches of base-pairing occur, producing loops. See poly AU. In all types of cells there are three kinds of RNA:

(1) Ribosomal RNA (rRNA) forms about 80% of the total. It is of high molecular weight and is metabolically stable. It is of two main types. See ribosomes.

(2) Transfer RNA (tRNA) forms about 15% of the total. Mol. wt. 23000-28000. There are tRNA molecules specific for each amino acid and on each molecule is an anticodon that locates to a codon on the mRNA and so brings the amino acids into correct sequence in the polypeptide being formed.

(3) Messenger RNA(mRNA) forms about 5% of the total and has a base composition corresponding very closely to DNA. The DNA base sequences transcribed and processed into mRNA determine the sequence of amino acids in the polypeptide chain.

Almost all plant virus species, and a majority of animal virus species, use RNA rather than DNA as their genetic material. RNA may also play a regulatory role in expression at the post-transcriptional level.

Altuvia S and Wagner GH (2000) Proc Natl Acad Sci 97, 9824

Eaton BE and Pieken WA (1995) Annu Rev Biochem 64, 837

ribonucleoprotein A complex comprising ribonucleic acid and protein, usually linked by electrostatic bonds.

ribonucleoside A purine or pyrimidine base covalently bound to a d-ribose sugar molecule. See nucleic acid.

ribonucleotide A ribonucleoside with one or more phosphate groups esterified to the 5' position of the sugar moiety. See nucleic acid.

ribonucleotide reductase (RR) An enzyme that catalyzes the conversion of ribonu-cleoside diphosphates to deoxyribo-nucleoside diphosphates.

ribose The sugar of ribonucleotides. See nucleic acid.

ribosomal frameshifting A purposeful shift in reading frame whereby ribo-somes respond to signals in the mRNA and move into a new reading frame (usually -1) at a specific point and continue translation in the new reading frame. Used in several virus mRNAs, especially by retroviruses, astroviruses and coronaviruses. May involve a pseudoknot in the mRNA or a shifty or slippery sequence, or both.

Brierley I (1995) J Gen Virol 76, 1885

0 0

Post a comment