Krüger D H, Barcak G J, Reuter M, Smith H O
Institute of Virology, Humboldt University School of Medicine (Charité), Berlin, GDR.
Nucleic Acids Res. 1988 May 11;16(9):3997-4008. doi: 10.1093/nar/16.9.3997.
EcoRII restriction sites [5'-CC(A/T)GG] in phage T3 and T7 DNA are refractory to cleavage by EcoRII, but become sensitive to cleavage in the presence of DNAs which contain an abundance of EcoRII sensitive sites (e.g. pBR322 or lambda DNA). Studies using fragments of pBR322 containing different numbers of EcoRII sites show that the susceptibility to EcoRII cleavage is proportional to the number of sites in the individual fragment. We postulate that EcoRII is the prototype of restriction endonucleases which require at least 2 simultaneously bound substrate sites for their activation. EcoRII sites are refractory when they occur at relatively low frequency in the DNA. The restriction enzyme can be activated by DNA with a higher frequency of sites.
噬菌体T3和T7 DNA中的EcoRII限制位点[5'-CC(A/T)GG]对EcoRII的切割具有抗性，但在存在大量EcoRII敏感位点的DNA（如pBR322或λ DNA）时，会变得对切割敏感。使用含有不同数量EcoRII位点的pBR322片段进行的研究表明，对EcoRII切割的敏感性与单个片段中的位点数量成正比。我们推测EcoRII是限制内切酶的原型，其激活需要至少2个同时结合的底物位点。当EcoRII位点在DNA中以相对较低的频率出现时，它们具有抗性。具有较高位点频率的DNA可以激活限制酶。
