title: Rnr4p, a novel ribonucleotide reductase small-subunit protein.
abstract: Ribonucleotide reductases catalyze the formation of deoxyribonucleotides by the reduction of the corresponding ribonucleotides. Eukaryotic ribonucleotide reductases are alpha2beta2 tetramers; each of the larger, alpha subunits possesses binding sites for substrate and allosteric effectors, and each of the smaller, beta subunits contains a binuclear iron complex. The iron complex interacts with a specific tyrosine residue to form a tyrosyl free radical which is essential for activity. Previous work has identified two genes in the yeast Saccharomyces cerevisiae, RNR1 and RNR3, that encode alpha subunits and one gene, RNR2, that encodes a beta subunit. Here we report the identification of a second gene from this yeast, RNR4, that encodes a protein with significant similarity to the beta-subunit proteins. The phenotype of rnr4 mutants is consistent with that expected for a defect in ribonucleotide reductase; rnr4 mutants are supersensitive to the ribonucleotide reductase inhibitor hydroxyurea and display an S-phase arrest at their restrictive temperature. rnr4 mutant extracts are deficient in ribonucleotide reductase activity, and this deficiency can be remedied by the addition of exogenous Rnr4p. As is the case for the other RNR genes, RNR4 is induced by agents that damage DNA. However, Rnr4p lacks a number of sequence elements thought to be essential for iron binding, and mutation of the critical tyrosine residue does not affect Rnr4p function. These results suggest that Rnr4p is catalytically inactive but, nonetheless, does play a role in the ribonucleotide reductase complex.
authors.affiliation: Section of Biochemistry, Molecular and Cell Biology, Cornell University, Ithaca, New York 14853, USA.
authors.forename: P J
authors.initials: PJ
authors.lastname: Wang
authors.forename: A
authors.initials: A
authors.lastname: Chabes
authors.forename: R
authors.initials: R
authors.lastname: Casagrande
authors.forename: X C
authors.initials: XC
authors.lastname: Tian
authors.forename: L
authors.initials: L
authors.lastname: Thelander
authors.forename: T C
authors.initials: TC
authors.lastname: Huffaker
mesh_terms: D000595:Amino Acid Sequence; D003001:Cloning, Molecular; D003080:Cold Temperature; D004791:Enzyme Inhibitors / Q000494:pharmacology; D018628:Gene Dosage; D015966:Gene Expression Regulation, Fungal / Q000502:physiology; D005800:Genes, Fungal / Q000235:genetics* / Q000502:physiology; D006918:Hydroxyurea / Q000494:pharmacology; D008741:Methyl Methanesulfonate / Q000494:pharmacology; D008969:Molecular Sequence Data; D009153:Mutagens / Q000494:pharmacology; D009154:Mutation; D010641:Phenotype; D012331:RNA, Fungal / Q000096:biosynthesis; D012333:RNA, Messenger / Q000096:biosynthesis; D012262:Ribonucleoside Diphosphate Reductase / Q000037:antagonists & inhibitors / Q000235:genetics*; D012264:Ribonucleotide Reductases / Q000037:antagonists & inhibitors / Q000235:genetics*; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000235:genetics*; D029701:Saccharomyces cerevisiae Proteins / Q000037:antagonists & inhibitors / Q000235:genetics*; D017386:Sequence Homology, Amino Acid
chemical_list: D004791:Enzyme Inhibitors; D009153:Mutagens; D012331:RNA, Fungal; D012333:RNA, Messenger; D029701:Saccharomyces cerevisiae Proteins; D008741:Methyl Methanesulfonate; D012264:Ribonucleotide Reductases; D012262:Ribonucleoside Diphosphate Reductase; C523202:Rnr4 protein, S cerevisiae; D006918:Hydroxyurea