Maxwell A, Halford S E
Biochem J. 1982 Apr 1;203(1):85-92. doi: 10.1042/bj2030085.
The cleavage of supercoiled DNA of plasmid pMB9 by restriction endonuclease SalGI has been studied. Under the optimal conditions for this reaction, the only product is the linear form of the DNA, in which both strands of the duplex have been cleaved at the SalGI recognition site. DNA molecules cleaved in one strand at this site were found to be poor substrates for the SalGI enzyme. Thus, both strands of the DNA appear to be cleaved in a concerted reaction. However, under other conditions, the enzyme cleaves either one or both strands of the DNA; the supercoiled substrate is then converted to either open-circle or linear forms, the two being produced simultaneously rather than consecutively. We propose a mechanism for the SalGI restriction endonuclease which accounts for the reactions of this enzyme under both optimal and other conditions. These reactions were unaffected by the tertiary structure of the DNA.
对限制性内切酶SalGI切割质粒pMB9的超螺旋DNA进行了研究。在该反应的最佳条件下，唯一的产物是DNA的线性形式，其中双链的两条链均在SalGI识别位点处被切割。发现在该位点单链被切割的DNA分子是SalGI酶的不良底物。因此，DNA的两条链似乎是在协同反应中被切割的。然而，在其他条件下，该酶会切割DNA的一条链或两条链；然后超螺旋底物会转化为开环或线性形式，这两种形式是同时产生而非相继产生的。我们提出了一种SalGI限制性内切酶的作用机制，该机制解释了该酶在最佳条件和其他条件下的反应。这些反应不受DNA三级结构的影响。
