LaBonne S G, Dumas L B
Biochemistry. 1983 Jun 21;22(13):3214-9. doi: 10.1021/bi00282a027.
We sought a protein from yeast that would bind more strongly to single-stranded DNA than to duplex DNA and would stimulate the activity of the major yeast DNA polymerase, but not polymerases from other organisms. We isolated a protein that binds about 200 times more strongly to single-stranded DNA than duplex DNA and stimulates yeast DNA polymerase I activity 4-5-fold. It inhibits synthesis catalyzed by calf thymus DNA polymerase alpha and has little effect on T4 DNA polymerase. This yeast protein, SSB-1, has a molecular weight of approximately 40 000. At apparent saturation there is one protein molecule bound per 40 nucleotides. Protein binding causes the single-stranded DNA molecule to assume a relatively extended conformation. It binds to single-stranded RNA as strongly as to DNA. SSB-1 increases the initial rate of polymerization catalyzed by yeast DNA polymerase I apparently by increasing the processivity of the enzyme. We estimate there are 7500-30 000 molecules of SSB-1 per yeast cell, enough to bind at least 400-1600 nucleotides per replication fork. Thus it is present in sufficient abundance to participate in DNA replication in vivo in the manner suggested by these in vitro experiments.
我们寻找一种来自酵母的蛋白质，该蛋白质与单链DNA的结合力要比与双链DNA的结合力更强，并且能够刺激酵母主要DNA聚合酶的活性，但对其他生物体的聚合酶没有作用。我们分离出一种蛋白质，它与单链DNA的结合力比与双链DNA的结合力强约200倍，并能将酵母DNA聚合酶I的活性提高4至5倍。它抑制小牛胸腺DNA聚合酶α催化的合成，而对T4 DNA聚合酶几乎没有影响。这种酵母蛋白SSB - 1的分子量约为40000。在明显饱和时，每40个核苷酸结合一个蛋白质分子。蛋白质结合使单链DNA分子呈现出相对伸展的构象。它与单链RNA的结合力与和DNA的结合力一样强。SSB - 1显然是通过提高酶的持续合成能力来提高酵母DNA聚合酶I催化的聚合反应的初始速率。我们估计每个酵母细胞中有7500 - 30000个SSB - 1分子，足以在每个复制叉处结合至少400 - 1600个核苷酸。因此，它的丰度足以按照这些体外实验所表明的方式参与体内DNA复制。
