Disease relevance of RNR3

• Simultaneous overexpression of RNR2, RNR3 and RNR4 partially rescued the HU hypersensitivity of a ccr4Delta dun1Delta strain, consistent with the notion that the RNR genes are key targets of Crt1 [1].
• These strains carried stably integrated fusions of RNR3 or RAD54 promoters to the E. coli beta-glucuronidase GUS gene [2].

High impact information on RNR3

• We investigated the mechanism by which DNA damage induces transcription of RNR3, a subunit of ribonucleotide reductase [3].
• Inactivation of this domain abolished DNA damage-dependent Rad53 phosphorylation, G2/M cell cycle phase arrest, and increase of RNR3 transcription but did not affect replication inhibition-dependent Rad53 phosphorylation [4].
• SWI/SNF-dependent chromatin remodeling of RNR3 requires TAF(II)s and the general transcription machinery [5].
• Examination of the inducibility of RNR3 in response to UV damage has revealed that the various checkpoint genes can be arranged in a pathway consistent with their requirement to arrest cells at different stages of the cell cycle [6].
• RNR1 is inducible 3- to 5-fold, and RNR3 is inducible greater than 100-fold [7].

Biological context of RNR3

• Mutants defective for both pathways are severely deficient in Rad53p phosphorylation and RNR3 induction and are significantly more sensitive to DNA damage and replication blocks than single mutants alone [6].
• Yet an rnr3 null mutant has no obvious phenotype even under DNA damaging conditions, and the contribution of RNR3 to ribonucleotide reduction is not clear [8].
• To probe the signaling pathway mediating this DNA damage response, we have designed a general selection system for isolating spontaneous trans-acting mutations that alter RNR3 expression using a chromosomal RNR3-URA3 transcriptional fusion and an RNR3-lacZ reporter plasmid [9].
• When MATa cells are arrested in G1 by alpha-factor, RNR1 and RNR3 mRNA is still inducible by DNA damage, indicating that the observed induction can occur outside of S phase [7].
• At earlier stages of growth, as the telomerase-deficient cells began to show loss of growth potential, the cells arrested in G2/M and showed RNR3 induction and Rad53p phosphorylation [10].

Associations of RNR3 with chemical compounds

• Both RNR1 and RNR3 transcripts are inducible by treatments that damage DNA, such as 4-nitroquinoline-1-oxide and methylmethanesulfonate, or block DNA replication, such as hydroxyurea [7].
• All mutations affecting the inter-zinc finger amino acids or the zinc fingers themselves are sensitive to methylmethane sulfonate and have reduced ability to induce RNR3, showing that the mutants are defective in the transcriptional response to DNA damage as well as the cell cycle response [11].
• In control yeast, no induction of RNR3 was observed upon exposure to 2-aminofluorene or aflatoxin B1 [12].
• Exposure to 2-acetylaminofluorene or benzo[a]pyrene did not lead to induction of RNR3 in yeast expressing CYP1A1 [12].
• Various drugs that cause DNA damage effectively induced RNR3 expression; alkylating agents (cisplatin, mitomycin C and N-methyl-N'-nitro-N-nitrosoguanidine), a radical producer (bleomycin), and an intercalator (actinomycin D) induced RNR3 [12].

Regulatory relationships of RNR3

• Yeast DNA damage-inducible Rnr3 has a very low catalytic activity strongly stimulated after the formation of a cross-talking Rnr1/Rnr3 complex [8].
• Furthermore, Tup1 repressed RNR3 and blocked preinitiation complex formation in the Deltaisw2 mutant, even though nucleosome positioning was completely disrupted over the promoter and ORF [13].

Other interactions of RNR3

• 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 [14].
• The lethality of RNR4 deletion mutations can be suppressed by overexpression of RNR1 and RNR3, two genes encoding the large subunit of the RNR enzyme, indicating genetic interactions among the RNR genes [15].
• Furthermore, the inducibility of RNR3 transcription in response to DNA damage is dependent on RFC5 [16].
• The in vitro activity of Rnr3 was less than 1% of the Rnr1 activity [8].
• Here, we demonstrate that both ISW2 and TUP1 are required to position nucleosomes across the entire coding sequence of the DNA damage-inducible gene RNR3 [13].

Analytical, diagnostic and therapeutic context of RNR3

• Enzyme inactivation increased cellular radiosensitivity, blocked the restitution of broken chromosomes, assayed by pulsed-field gel electrophoresis, and prolonged the induction of a DNA damage-inducible gene (RNR3) [17].
• Chromatin immunoprecipitation (ChIP) experiments show that TBP, pol II and Set1p recruitment to the activated RNR3 locus is defective in cells lacking NOT4 [18].

References