ISOLATION AND CHARACTERIZATION OF GENE 5 PROTEIN OF FILAMENTOUS BACTERIAL VIRUSES
ISOLATION AND CHARACTERIZATION OF GENE 5 PROTEIN OF FILAMENTOUS BACTERIAL VIRUSES
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DOI：
10.1016/0022-2836(72)90269-0
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发表时间：
1972-01-01
影响因子：
5.6
通讯作者：
DELIUS, H
中科院分区：
文献类型：
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作者：
ALBERTS, B;FREY, L;DELIUS, H
丝状噬菌体基因5的产物是合成单链子代DNA所必需的。当从感染噬菌体fd或M13的大肠杆菌中提取的提取物在单链DNA/纤维素上层析时，可以洗脱出分子量约为10，000道尔顿的DNA结合蛋白，并且每个细胞至少有100，000个拷贝。该蛋白质在噬菌体M13的琥珀型突变体5-H3和温度敏感型突变体5-HS 1中发生改变，这将其鉴定为基因5产物（亨利和普拉特，1969）。如通过在4 °C下的蔗糖梯度沉降所判断的，纯蛋白质与单链DNA紧密且协同地结合，但不与双链DNA结合;在饱和时，每4个DNA核苷酸结合一个蛋白质单体。这种选择性的DNA结合使基因5蛋白能够在生理温度下迅速使双链DNA变性。在这些方面，基因5蛋白类似于前述T4噬菌体基因32蛋白，T4噬菌体DNA的复制和重组都需要该蛋白。然而，电子显微镜显示，基因5蛋白与单链DNA的复合物的结构是完全不同的：而基因32蛋白迫使DNA进入延伸的线性构象，基因5蛋白将两个蛋白质覆盖的DNA结合成螺旋状，棒状结构。由于这个原因和其他原因，这两种“DNA解旋”蛋白在复制过程中可能具有完全不同的作用。
The product of gene 5 of filamentous bacteriophages is required for synthesis of the single-stranded progeny DNA. When extracts made fromEscherichia coliinfected with bacteriophages fd or M13 are chromatographed on single-stranded DNA/cellulose, a DNA-binding protein can be eluted which has a molecular weight of about 10,000 daltons and is made in at least 100,000 copies per cell. This protein is altered in amber mutant5-H3and temperature-sensitive mutant5-HS1of phage M13, which identifies it as the gene 5 product (Henry & Pratt, 1969). As judged by sucrose-gradient sedimentation at 4 °C, the pure protein binds tightly and co-operatively to single-stranded, but not to double-stranded, DNA's; at saturation, one protein monomer is bound per every 4 DNA nucleotides. This selective DNA-binding enables the gene 5 protein to denature double-stranded DNA's rapidly at physiological temperatures. In these respects, the gene 5 protein resembles the T4 bacteriophage gene 32 protein described previously, a protein which is required for both the replication and recombination of T4 bacteriophage DNA. However, electron microscopy reveals that the structure of the gene 5 protein complex with single-stranded DNA is quite different: whereas gene 32 protein forces the DNA into an extended linear conformation, the gene 5 protein coalesces two protein-covered DNA stands into a helical, rodlike structure. For this and other reasons, these two “DNA unwinding” proteins could have quite different roles in the replication process.