Slatko B E, Benner J S, Jager-Quinton T, Moran L S, Simcox T G, Van Cott E M, Wilson G G
New England Biolabs, Inc., Beverly, MA 01915.
Nucleic Acids Res. 1987 Dec 10;15(23):9781-96. doi: 10.1093/nar/15.23.9781.
The Taq I modification and restriction genes (recognition sequence TCGA) have been cloned in E. coli and their DNA sequences have been determined. Both proteins were characterized and the N-terminal sequence of the endonuclease was determined. The genes have the same transcriptional orientation with the methylase gene 5' to the endonuclease gene. The methylase gene is 1089 bp in length (363 amino acids, 40,576 daltons); the endonuclease gene is 702 bp in length (234 amino acids, 27,523 daltons); they are separated by 132 bp. Both methylase and endonuclease activity can be detected in cell extracts. The clones fully modify the vector and chromosomal DNA but they fail to restrict infecting phage. Clones carrying only the restriction gene are viable even in the absence of modification. The restriction gene contains 7 Taq I sites; the modification gene contains none. This asymmetric distribution of sites could be important in the regulation of the expression of the endonuclease gene.
Taq I甲基化和限制酶基因（识别序列为TCGA）已在大肠杆菌中克隆出来，并测定了它们的DNA序列。对这两种蛋白质进行了表征，并确定了核酸内切酶的N端序列。这些基因与甲基化酶基因具有相同的转录方向，甲基化酶基因在核酸内切酶基因的5'端。甲基化酶基因长度为1089 bp（363个氨基酸，40576道尔顿）；核酸内切酶基因长度为702 bp（234个氨基酸，27523道尔顿）；它们之间相隔132 bp。在细胞提取物中可检测到甲基化酶和核酸内切酶的活性。这些克隆可完全修饰载体和染色体DNA，但它们不能限制感染的噬菌体。即使在没有甲基化的情况下，仅携带限制酶基因的克隆也是可行的。限制酶基因含有7个Taq I位点；甲基化酶基因不含Taq I位点。这种位点的不对称分布可能在核酸内切酶基因表达的调控中起重要作用。
