Wiekowski M, Schwarz M W, Stahl H
Fakultät für Biologie, Universität Konstanz, Federal Republic of Germany.
J Biol Chem. 1988 Jan 5;263(1):436-42.
The ATPase of SV40 large T antigen (T antigen) which is essential for the replication of SV40 minichromosomes was recently shown to be functionally related to a newly discovered DNA helicase activity. The T antigen helicase unwinds DNA duplices of several kilobase pairs in a reaction depending on the presence of hydrolyzable ribo- or deoxyribonucleoside triphosphates. The in vitro rate of movement through duplex DNA was found to be about 100 base pairs/min at 37 degrees C. For DNA unwinding, T antigen requires a 3'-single strand extension of a partially double-stranded substrate and invades the double strand section processively, in a 3' to 5' direction. The minimum length of the single-stranded tail was determined to be less than 5 nucleotides. Unwinding studies in the presence of the Escherichia coli single strand-specific DNA-binding protein and competition experiments indicate that T antigen helicase binds preferentially at the single-stranded/double-stranded DNA junction. This DNA structure is therefore proposed to serve as an entry site for the T antigen helicase. Previously reported data suggest that T antigen is the replicative helicase of the SV40 minichromosome. The results presented here are consistent with these findings and imply that T antigen migrates actively and processively along the template for the leading strand.
SV40 大 T 抗原（T 抗原）的 ATP 酶对 SV40 微型染色体的复制至关重要，最近发现它在功能上与新发现的 DNA 解旋酶活性相关。T 抗原解旋酶在依赖于可水解的核糖或脱氧核糖核苷三磷酸存在的反应中解开几千碱基对的 DNA 双链。在 37℃下，通过双链 DNA 的体外移动速率约为每分钟 100 个碱基对。对于 DNA 解旋，T 抗原需要部分双链底物的 3' 单链延伸，并以 3' 到 5' 方向连续侵入双链部分。单链尾巴的最小长度被确定为小于 5 个核苷酸。在大肠杆菌单链特异性 DNA 结合蛋白存在下的解旋研究和竞争实验表明，T 抗原解旋酶优先结合在单链/双链 DNA 交界处。因此，这种 DNA 结构被认为是 T 抗原解旋酶的进入位点。先前报道的数据表明，T 抗原是 SV40 微型染色体的复制性解旋酶。这里呈现的结果与这些发现一致，并暗示 T 抗原沿着前导链模板积极且连续地迁移。
