Brooks J E, Roberts R J
Nucleic Acids Res. 1982 Feb 11;10(3):913-34. doi: 10.1093/nar/10.3.913.
DNAs were prepared from twenty-six bacterial species and digested with a variety of restriction endonucleases to determine what modifications the DNAs carry. Several general conclusions could be made: 1) First, in no instance was the DNA of a restriction enzyme. 2) The specificity of the DNA modification was the same as that of its restriction counterpart; there were no cases of the DNAs being modified against a less specific class of restriction enzymes. 3) In most (but not all) cases, the resistance of a bacterium's DNA to its own restriction enzyme could be generalized to include resistance to all other restriction enzymes with the same specificity (isoschizomers). 4) DNA modified within the central tetramer of a recognition sequence is usually protected against cleavage by all related hexameric enzymes possessing that central tetramer. Only three families of DNA presented in this study disobey this rule. 5) Finally, a significant number of cases emerge where bacterial DNA carries a modification but no corresponding restriction endonuclease activity.
从26种细菌中提取DNA，并使用多种限制性内切酶进行消化，以确定DNA携带了哪些修饰。可以得出几个一般性结论：1）首先，在任何情况下，DNA都不是限制性酶。2）DNA修饰的特异性与其限制性对应物相同；不存在针对特异性较低的限制性酶类别对DNA进行修饰的情况。3）在大多数（但不是所有）情况下，细菌DNA对自身限制性酶的抗性可以推广到包括对所有具有相同特异性的其他限制性酶（同裂酶）的抗性。4）在识别序列的中央四聚体内修饰的DNA通常受到所有具有该中央四聚体的相关六聚体酶切割的保护。本研究中仅呈现的三个DNA家族不遵守此规则。5）最后，出现了大量细菌DNA携带修饰但没有相应限制性内切酶活性的情况。
