Horiuchi K, Zinder N D
Proc Natl Acad Sci U S A. 1972 Nov;69(11):3220-4. doi: 10.1073/pnas.69.11.3220.
We studied the cleavage of the replicative-form DNA (RF I) of bacteriophage f1 and its SB mutants by purified restriction endonuclease of E. coli B. The results indicate that: (i) Circular replicative forms are broken once to yield full-length linear molecules (RF III). Such linear molecules are less susceptible than RF I to endonuclease R-B. (ii) The genetic sites (SB sites) that confer on the DNA susceptibility to B-restriction are not the actual sites of cleavage. The number of possible cleavage sites is larger than the number of SB sites. We conclude this because an RF III molecule produced by endonuclease R-B from RF I of a mutant that has only one SB site can be circularized by denaturation and renaturation. (iii) The SB site is not modified when the DNA is cleaved, since an SB site can be used repeatedly by endonuclease R-B; the RF III described in ii can be cleaved by the same enzyme after denaturation and renaturation.
我们研究了用大肠杆菌B纯化的限制性内切核酸酶对噬菌体f1及其SB突变体的复制型DNA（RF I）的切割。结果表明：（i）环状复制型被切割一次产生全长线性分子（RF III）。这种线性分子比RF I对内切核酸酶R-B的敏感性更低。（ii）赋予DNA对B-限制敏感性的遗传位点（SB位点）不是实际的切割位点。可能的切割位点数大于SB位点数。我们得出这个结论是因为内切核酸酶R-B从只有一个SB位点的突变体的RF I产生的RF III分子可以通过变性和复性环化。（iii）DNA被切割时SB位点未被修饰，因为SB位点可被内切核酸酶R-B重复使用；ii中描述的RF III在变性和复性后可被同一种酶切割。
