Rice A C, Ficht T A, Holladay L A, Moyer R W
J Biol Chem. 1979 Aug 25;254(16):8042-51.
We have purified a DNA-binding protein from bacteriophage T5-infected cells. The protein is the product of the T5 gene D5 and is produced in quantities ultimately exceeding 2% of the total cell protein. The protein has no tendency to aggregate and exists in solution as a monomer of about 29,000 daltons. Although the protein binds with a high affinity to both single-stranded (fd, T7) and duplex DNA (T5, T7), there is a preferred binding to duplex DNA. The binding of the gene D5 protein to duplex DNA is cooperative with an estimated dissociation constant of 6.27 x 10(-10) M and leads to the production of a more condensed form of the DNA. In contrast, binding of the gene D5 protein to single-stranded DNA is noncooperative with an estimated dissociation constant of only 1.85 x 10(-8) M and produces a sedimentation shift in the DNA proportional to the added mass of the protein. The protein product of the gene D5 of bacteriophage T5 is known to be required for both T5 DNA replication and for the inhibition of early phage gene expression. We also show here that the protein is required to initiate transcription of the late region of the T5 genome.
我们从感染噬菌体T5的细胞中纯化出了一种DNA结合蛋白。该蛋白是T5基因D5的产物，其产量最终超过细胞总蛋白的2%。该蛋白没有聚集倾向，以约29,000道尔顿的单体形式存在于溶液中。尽管该蛋白与单链（fd、T7）和双链DNA（T5、T7）都有高亲和力结合，但它更倾向于与双链DNA结合。基因D5蛋白与双链DNA的结合具有协同性，估计解离常数为6.27×10⁻¹⁰ M，并导致DNA形成更浓缩的形式。相比之下，基因D5蛋白与单链DNA的结合不具有协同性，估计解离常数仅为1.85×10⁻⁸ M，并且会使DNA的沉降发生与添加的蛋白质量成比例的变化。已知噬菌体T5的基因D5的蛋白产物对于T5 DNA复制和早期噬菌体基因表达的抑制都是必需的。我们在此还表明，该蛋白是启动T5基因组晚期区域转录所必需的。
