Biswas I, Maguin E, Ehrlich S D, Gruss A
Laboratoire de Génétique Microbienne, Institut National de la Recherche Agronomique, Jouy en Josas, France.
Proc Natl Acad Sci U S A. 1995 Mar 14;92(6):2244-8. doi: 10.1073/pnas.92.6.2244.
Linear DNA molecules are subject to degradation by various exonucleases in vivo unless their ends are protected. It has been demonstrated that a specific 8-bp sequence, 5'-GCTGGTGG-3', named Chi, can protect linear double-stranded DNA from the major Escherichia coli exonuclease RecBCD. Chi protects linear replication products of rolling-circle plasmids from RecBCD degradation in vivo, in agreement with observations in vitro. A unique 7-bp sequence, 5'-GCGCGTG-3', is shown to protect similar replication products from degradation in Lactococcus lactis strains but not in more distantly related Gram-positive bacteria. The properties of this sequence in L. lactis correspond to those of a Chi site. Linear plasmid replication products have been detected in numerous prokaryotes, suggesting the widespread existence of short species-specific sequences that preserve linear DNA from extensive degradation by host cell exonucleases.
线性DNA分子在体内会受到各种核酸外切酶的降解，除非其末端受到保护。已经证明，一种特定的8碱基对序列5'-GCTGGTGG-3'，称为Chi，可保护线性双链DNA免受大肠杆菌主要核酸外切酶RecBCD的降解。Chi在体内保护滚环质粒的线性复制产物免受RecBCD降解，这与体外观察结果一致。一个独特的7碱基对序列5'-GCGCGTG-3'被证明可保护乳酸乳球菌菌株中的类似复制产物不被降解，但在亲缘关系较远的革兰氏阳性细菌中则不能。该序列在乳酸乳球菌中的特性与Chi位点的特性相对应。在许多原核生物中都检测到了线性质粒复制产物，这表明广泛存在短的物种特异性序列，这些序列可保护线性DNA不被宿主细胞核酸外切酶广泛降解。
