RNR4/YGR180C Summary Help

Standard Name RNR4 1, 2
Systematic Name YGR180C
Alias CRT3 3 , PSO3 4 , 5 , 6
Feature Type ORF, Verified
Description Ribonucleotide-diphosphate reductase (RNR) small subunit; the RNR complex catalyzes the rate-limiting step in dNTP synthesis and is regulated by DNA replication and DNA damage checkpoint pathways via localization of the small subunits; relocalizes from nucleus to cytoplasm upon DNA replication stress; RNR4 has a paralog, RNR2, that arose from the whole genome duplication (7, 8, 9 and see Summary Paragraph)
Name Description RiboNucleotide Reductase 2
Chromosomal Location
ChrVII:856301 to 855264 | ORF Map | GBrowse
Note: this feature is encoded on the Crick strand.
Gene Ontology Annotations All RNR4 GO evidence and references
  View Computational GO annotations for RNR4
Molecular Function
Manually curated
Biological Process
Manually curated
Cellular Component
Manually curated
Regulators 11 genes
Classical genetics
Large-scale survey
124 total interaction(s) for 88 unique genes/features.
Physical Interactions
  • Affinity Capture-MS: 23
  • Affinity Capture-RNA: 1
  • Affinity Capture-Western: 9
  • Biochemical Activity: 2
  • Co-crystal Structure: 2
  • Co-localization: 3
  • Co-purification: 2
  • PCA: 3
  • Protein-peptide: 5
  • Reconstituted Complex: 17
  • Two-hybrid: 4

Genetic Interactions
  • Dosage Lethality: 1
  • Dosage Rescue: 2
  • Phenotypic Enhancement: 2
  • Phenotypic Suppression: 3
  • Synthetic Growth Defect: 16
  • Synthetic Lethality: 29

Expression Summary
Length (a.a.) 345
Molecular Weight (Da) 40,054
Isoelectric Point (pI) 4.96
Phosphorylation PhosphoGRID | PhosphoPep Database
sequence information
ChrVII:856301 to 855264 | ORF Map | GBrowse
Note: this feature is encoded on the Crick strand.
Last Update Coordinates: 2011-02-03 | Sequence: 1996-07-31
Subfeature details
Most Recent Updates
Coordinates Sequence
CDS 1..1038 856301..855264 2011-02-03 1996-07-31
Retrieve sequences
Analyze Sequence
S288C only
S288C vs. other species
S288C vs. other strains
External Links All Associated Seq | E.C. | Entrez Gene | Entrez RefSeq Protein | MIPS | Search all NCBI (Entrez) | UniProtKB
Primary SGDIDS000003412

Ribonucleotide reductase (RNR) is a tetrameric protein complex that catalyzes the conversion of nucleotides to deoxynucleotides, the rate-limiting step in de novo deoxyribonucleotide biosynthesis, and plays an essential role in DNA replication and repair (10, 7, 11). A balanced supply of deoxyribonucleoside triphosphates (dNTPs) is required for accurate genome duplication. Both the overall concentration and the balance among the individual dNTPs (dATP, dTTP, dGTP, and dCTP) are tightly regulated by ribonucleotide reductase (12). Ribonucleotide reductase activity is periodic during the cell cycle, rising from an initial low level to a maximum early in S phase, then declining at the end of S phase (13).

Ribonucleotide reductase consists of two large and two small subunits. In Saccharomyces cerevisiae, the main isoform of the large subunit is encoded by RNR1 and another isoform by RNR3; the two small subunits are encoded by RNR2 and RNR4 (7, 14). The Rnr1p:Rnr1p homodimer contains the regulatory and catalytic sites, and the Rnr2p:Rnr4p heterodimer houses the essential diferric-tyrosyl radical cofactor (15). The crucial role of Rnr4p is to fold correctly and stabilize the radical-storing Rnr2p by forming a stable 1:1 Rnr2p/Rnr4p complex (16, 17). The contribution of RNR3 to ribonucleotide reduction is not clear (18). RNR3 is not expressed during normal growth, but like the other three subunits, is strongly induced by DNA damage, though never reaching more than one-tenth of the Rnr1p levels (19, 18).

During most of the cell cycle, Rnr1p and Rnr3p are localized to the cytoplasm, while Rnr2p and Rnr4p are present in the nucleus. In response to S phase or DNA damage, the Rnr2p:Rnr4p subcomplex undergoes checkpoint-dependent, nucleus-to-cytoplasm redistribution and binds the Rnr1p homodimer, forming an active RNR complex (7, 11, 20). Dif1p controls subcellular localization of the Rnr2p:Rnr4p subcomplex by binding directly to it and mediating its nuclear import (21, 20). Wtm1p acts as a nuclear anchor to maintain nuclear localization of Rnr2p:Rnr4p outside of S phase or in the absence of DNA damage (22, 23, 20).

Inhibition of ribonucleotide reductase activity by hydroxyurea treatment results in S phase cell-cycle arrest and large-budded, uninucleate cells (24, 2). Both RNR1 and RNR2 are essential for viability, whereas RNR3 is not (24, 25). Temperature-sensitive alleles of RNR1 and RNR2 arrest with a large-budded, cdc terminal phenotype at the nonpermissive temperature (3). Overexpression of RNR3 suppresses the lethality of rnr1 null mutations (24, 25). Cells deleted for RNR3 are hypersensitive to rapamycin plus MMS (26). Deletion of RNR4 is lethal is some strain backgrounds but not in others, and this lethality can be suppressed by overexpression of RNR1 and RNR3 (1), or of RNR2 (14). Some rnr4 null mutants exhibit slow growth and sensitivity to mutagens, including UV light and psoralens, as well as increased sensitivity to oxidative stress (6, 14). rnr4 null mutant cells are increased in size and also show higher budding frequency, pointing to a delay of mitosis/cytokinesis (6, 14).

RNR has been identified in E. coli (27), plants (28) and mammals (29, 24, 27, 17). Because RNR activity is crucial for rapidly dividing cells, its overexpression can lead to neoplastic transformation, making RNR a target for cancer therapy (30). In mammalian cells, the RNR small subunit is the site of action of several antitumor agents, including hydroxyurea and 4-methyl-5-amino-1-formylisoquinoline thiosemicarbazone (MAIQ) (31, 32).

Last updated: 2010-09-13 Contact SGD

References cited on this page View Complete Literature Guide for RNR4
1) Huang M and Elledge SJ  (1997) Identification of RNR4, encoding a second essential small subunit of ribonucleotide reductase in Saccharomyces cerevisiae. Mol Cell Biol 17(10):6105-13
2) Wang PJ, et al.  (1997) Rnr4p, a novel ribonucleotide reductase small-subunit protein. Mol Cell Biol 17(10):6114-21
3) Zhou Z and Elledge SJ  (1992) Isolation of crt mutants constitutive for transcription of the DNA damage inducible gene RNR3 in Saccharomyces cerevisiae. Genetics 131(4):851-66
4) Henriques JA and Moustacchi E  (1980) Isolation and characterization of pso mutants sensitive to photo-addition of psoralen derivatives in Saccharomyces cerevisiae. Genetics 95(2):273-88
5) Brendel M, et al.  (2003) Role of PSO genes in repair of DNA damage of Saccharomyces cerevisiae. Mutat Res 544(2-3):179-93
6) Strauss M, et al.  (2007) RNR4 mutant alleles pso3-1 and rnr4Delta block induced mutation in Saccharomyces cerevisiae. Curr Genet 51(4):221-31
7) Yao R, et al.  (2003) Subcellular localization of yeast ribonucleotide reductase regulated by the DNA replication and damage checkpoint pathways. Proc Natl Acad Sci U S A 100(11):6628-33
8) Byrne KP and Wolfe KH  (2005) The Yeast Gene Order Browser: combining curated homology and syntenic context reveals gene fate in polyploid species. Genome Res 15(10):1456-61
9) Tkach JM, et al.  (2012) Dissecting DNA damage response pathways by analysing protein localization and abundance changes during DNA replication stress. Nat Cell Biol 14(9):966-76
10) Ge J, et al.  (2001) Why multiple small subunits (Y2 and Y4) for yeast ribonucleotide reductase? Toward understanding the role of Y4. Proc Natl Acad Sci U S A 98(18):10067-72
11) An X, et al.  (2006) Cotransport of the heterodimeric small subunit of the Saccharomyces cerevisiae ribonucleotide reductase between the nucleus and the cytoplasm. Genetics 173(1):63-73
12) Kumar D, et al.  (2010) Highly mutagenic and severely imbalanced dNTP pools can escape detection by the S-phase checkpoint. Nucleic Acids Res 38(12):3975-83
13) Lowdon M and VITOLS E  (1973) Ribonucleotide reductase activity during the cell cycle of Saccharomyces cerevisiae. Arch Biochem Biophys 158(1):177-84
14) Basso TS, et al.  (2008) Low productivity of ribonucleotide reductase in Saccharomyces cerevisiae increases sensitivity to stannous chloride. Genet Mol Res 7(1):1-6
15) Xu H, et al.  (2006) Structures of eukaryotic ribonucleotide reductase I define gemcitabine diphosphate binding and subunit assembly. Proc Natl Acad Sci U S A 103(11):4028-33
16) Chabes A, et al.  (2000) Yeast ribonucleotide reductase has a heterodimeric iron-radical-containing subunit. Proc Natl Acad Sci U S A 97(6):2474-9
17) Sommerhalter M, et al.  (2004) Structures of the yeast ribonucleotide reductase Rnr2 and Rnr4 homodimers. Biochemistry 43(24):7736-42
18) Domkin V, et al.  (2002) Yeast DNA damage-inducible Rnr3 has a very low catalytic activity strongly stimulated after the formation of a cross-talking Rnr1/Rnr3 complex. J Biol Chem 277(21):18574-8
19) Li B and Reese JC  (2001) Ssn6-Tup1 regulates RNR3 by positioning nucleosomes and affecting the chromatin structure at the upstream repression sequence. J Biol Chem 276(36):33788-97
20) Lee YD, et al.  (2008) Dif1 is a DNA-damage-regulated facilitator of nuclear import for ribonucleotide reductase. Mol Cell 32(1):70-80
21) Wu X and Huang M  (2008) Dif1 controls subcellular localization of ribonucleotide reductase by mediating nuclear import of the r2 subunit. Mol Cell Biol 28(23):7156-67
22) Zhang Z, et al.  (2006) Nuclear localization of the Saccharomyces cerevisiae ribonucleotide reductase small subunit requires a karyopherin and a WD40 repeat protein. Proc Natl Acad Sci U S A 103(5):1422-7
23) Lee YD and Elledge SJ  (2006) Control of ribonucleotide reductase localization through an anchoring mechanism involving Wtm1. Genes Dev 20(3):334-44
24) Elledge SJ and Davis RW  (1990) Two genes differentially regulated in the cell cycle and by DNA-damaging agents encode alternative regulatory subunits of ribonucleotide reductase. Genes Dev 4(5):740-51
25) Elledge SJ and Davis RW  (1987) Identification and isolation of the gene encoding the small subunit of ribonucleotide reductase from Saccharomyces cerevisiae: DNA damage-inducible gene required for mitotic viability. Mol Cell Biol 7(8):2783-93
26) Shen C, et al.  (2007) TOR signaling is a determinant of cell survival in response to DNA damage. Mol Cell Biol 27(20):7007-17
27) Elledge SJ, et al.  (1993) DNA damage and cell cycle regulation of ribonucleotide reductase. Bioessays 15(5):333-9
28) Yoo SC, et al.  (2009) Rice Virescent3 and Stripe1 Encoding the Large and Small Subunits of Ribonucleotide Reductase Are Required for Chloroplast Biogenesis during Early Leaf Development. Plant Physiol 150(1):388-401
29) Elledge SJ, et al.  (1992) Ribonucleotide reductase: regulation, regulation, regulation. Trends Biochem Sci 17(3):119-23
30) Abid MR, et al.  (1999) Translational regulation of ribonucleotide reductase by eukaryotic initiation factor 4E links protein synthesis to the control of DNA replication. J Biol Chem 274(50):35991-8
31) Rittberg DA and Wright JA  (1989) Relationships between sensitivity to hydroxyurea and 4-methyl-5-amino-1-formylisoquinoline thiosemicarbazone (MAIO) and ribonucleotide reductase RNR2 mRNA levels in strains of Saccharomyces cerevisiae. Biochem Cell Biol 67(7):352-7
32) Xu H, et al.  (2008) The Structural Basis for Peptidomimetic Inhibition of Eukaryotic Ribonucleotide Reductase: A Conformationally Flexible Pharmacophore. J Med Chem 51(15):4653-4659