Huang M, Elledge S J
Verna and Mars McLean Department of Biochemistry, Howard Hughes Medical Institute, Baylor College of Medicine, Houston, Texas 77030, USA.
Mol Cell Biol. 1997 Oct;17(10):6105-13. doi: 10.1128/MCB.17.10.6105.
Ribonucleotide reductase (RNR), which catalyzes the rate-limiting step for deoxyribonucleotide production required for DNA synthesis, is an alpha2beta2 tetramer consisting of two large and two small subunits. RNR2 encodes a small subunit and is essential for mitotic viability in Saccharomyces cerevisiae. We have cloned a second essential gene encoding a homologous small subunit, RNR4. RNR4 and RNR2 appear to have nonoverlapping functions and cannot substitute for each other even when overproduced. 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. RNR2 and RNR4 may be present in the same reductase complex in vivo, since they coimmunoprecipitate from cell extracts. Like the other RNR genes, RNR4 is inducible by DNA-damaging agents through the same signal transduction pathway involving MEC1, RAD53, and DUN1 kinase genes. Analysis of DNA damage inducibility of RNR2 and RNR4 revealed partial inducibility in dun1 mutants, indicating a DUN1-independent branch of the transcriptional response to DNA damage.
核糖核苷酸还原酶（RNR）催化DNA合成所需的脱氧核糖核苷酸生成的限速步骤，它是一种由两个大亚基和两个小亚基组成的α2β2四聚体。RNR2编码一个小亚基，对酿酒酵母的有丝分裂活力至关重要。我们克隆了第二个编码同源小亚基的必需基因RNR4。RNR4和RNR2似乎具有不重叠的功能，即使过量表达也不能相互替代。RNR4缺失突变的致死性可通过RNR1和RNR3的过表达来抑制，这两个基因编码RNR酶的大亚基，表明RNR基因之间存在遗传相互作用。RNR2和RNR4可能在体内存在于同一个还原酶复合物中，因为它们可从细胞提取物中共免疫沉淀。与其他RNR基因一样，RNR4可通过涉及MEC1、RAD53和DUN1激酶基因的相同信号转导途径被DNA损伤剂诱导。对RNR2和RNR4的DNA损伤诱导性分析显示，在dun1突变体中存在部分诱导性，表明对DNA损伤的转录反应存在一个不依赖DUN1的分支。
