Umezu K, Nakayama K, Nakayama H
Department of Microbiology, Faculty of Dentistry, Kyushu University, Fukuoka, Japan.
Proc Natl Acad Sci U S A. 1990 Jul;87(14):5363-7. doi: 10.1073/pnas.87.14.5363.
The Escherichia coli recQ gene, a member of the RecF recombination gene family, was set in an overexpression plasmid, and its product was purified to near-homogeneity. The purified RecQ protein exhibited a DNA-dependent ATPase and a helicase activity. Without DNA, no ATPase activity was detected. The capacity as ATPase cofactor varied with the type of DNA in the following order: circular single strand greater than linear single strand much greater than circular or linear duplex. As a helicase, RecQ protein displaced an annealed 71-base or 143-base single-stranded fragment from circular or linear phage M13 DNA, and the direction of unwinding seemed to be 3'----5' with respect to the DNA single strand to which the enzyme supposedly bound. Furthermore, the protein could unwind 143-base-pair blunt-ended duplex DNA at a higher enzyme concentration. It is concluded that RecQ protein is a previously unreported helicase, which might possibly serve to generate single-stranded tails for a strand transfer reaction in the process of recombination.
大肠杆菌recQ基因是RecF重组基因家族的成员之一，被置于一个过表达质粒中，其产物被纯化至近乎均一。纯化后的RecQ蛋白表现出依赖DNA的ATP酶活性和螺旋酶活性。没有DNA时，未检测到ATP酶活性。作为ATP酶辅因子的能力随DNA类型的不同而变化，顺序如下：环状单链大于线性单链，远大于环状或线性双链。作为一种螺旋酶，RecQ蛋白能从环状或线性噬菌体M13 DNA上置换出一段退火的71个碱基或143个碱基的单链片段，并且解旋方向相对于假定该酶结合的DNA单链似乎是3'→5'。此外，在较高的酶浓度下，该蛋白能够解开143个碱基对的平端双链DNA。结论是RecQ蛋白是一种以前未报道过的螺旋酶，它可能在重组过程中为链转移反应产生单链尾巴。
