Standart N M, Bray S J, George E L, Hunt T, Ruderman J V
J Cell Biol. 1985 Jun;100(6):1968-76. doi: 10.1083/jcb.100.6.1968.
In both clam oocytes and sea urchin eggs, fertilization triggers the synthesis of a set of proteins specified by stored maternal mRNAs. One of the most abundant of these (p41) has a molecular weight of 41,000. This paper describes the identification of p41 as the small subunit of ribonucleotide reductase, the enzyme that provides the precursors necessary for DNA synthesis. This identification is based mainly on the amino acid sequence deduced from cDNA clones corresponding to p41, which shows homology with a gene in Herpes Simplex virus that is thought to encode the small subunit of viral ribonucleotide reductase. Comparison with the B2 (small) subunit of Escherichia coli ribonucleotide reductase also shows striking homology in certain conserved regions of the molecule. However, our attention was originally drawn to protein p41 because it was specifically retained by an affinity column bearing the monoclonal antibody YL 1/2, which reacts with alpha-tubulin (Kilmartin, J. V., B. Wright, and C. Milstein, 1982, J. Cell Biol., 93:576-582). The finding that this antibody inhibits the activity of sea urchin embryo ribonucleotide reductase confirmed the identity of p41 as the small subunit. The unexpected binding of the small subunit of ribonucleotide reductase can be accounted for by its carboxy-terminal sequence, which matches the specificity requirements of YL 1/2 as determined by Wehland et al. (Wehland, J., H. C. Schroeder, and K. Weber, 1984, EMBO [Eur. Mol. Biol. Organ.] J., 3:1295-1300). Unlike the small subunit, there is no sign of synthesis of a corresponding large subunit of ribonucleotide reductase after fertilization. Since most enzymes of this type require two subunits for activity, we suspect that the unfertilized oocytes contain a stockpile of large subunits ready for combination with newly made small subunits. Thus, synthesis of the small subunit of ribonucleotide reductase represents a very clear example of the developmental regulation of enzyme activity by control of gene expression at the level of translation.
在蛤卵母细胞和海胆卵中，受精都会触发由储存的母体mRNA所指定的一组蛋白质的合成。其中最丰富的一种蛋白质（p41）分子量为41,000。本文描述了p41被鉴定为核糖核苷酸还原酶的小亚基，该酶为DNA合成提供必要的前体。这一鉴定主要基于从与p41对应的cDNA克隆推导的氨基酸序列，该序列与单纯疱疹病毒中的一个基因显示出同源性，该基因被认为编码病毒核糖核苷酸还原酶的小亚基。与大肠杆菌核糖核苷酸还原酶的B2（小）亚基比较也显示在分子的某些保守区域有显著同源性。然而，我们最初关注蛋白质p41是因为它被带有单克隆抗体YL 1/2的亲和柱特异性保留，该抗体与α-微管蛋白反应（Kilmartin, J. V., B. Wright, and C. Milstein, 1982, J. Cell Biol., 93:576 - 582）。该抗体抑制海胆胚胎核糖核苷酸还原酶活性这一发现证实了p41是小亚基。核糖核苷酸还原酶小亚基的意外结合可以用其羧基末端序列来解释，该序列与Wehland等人确定的YL 1/2的特异性要求相符（Wehland, J., H. C. Schroeder, and K. Weber, 1984, EMBO [Eur. Mol. Biol. Organ.] J., 3:1295 - 1300）。与小亚基不同，受精后没有相应的核糖核苷酸还原酶大亚基合成的迹象。由于这类大多数酶需要两个亚基才能发挥活性，我们怀疑未受精的卵母细胞含有大量准备与新合成的小亚基结合的大亚基储备。因此，核糖核苷酸还原酶小亚基的合成代表了通过在翻译水平控制基因表达来调控酶活性的一个非常明显的例子。
