Zavil'gel'skiĭ G B, Letuchaia T A, Rastorguev S M
Mol Biol (Mosk). 2004 Sep-Oct;38(5):901-6.
The transmissive plasmid IncI1 R64 contains the ardA gene encoding the ArdA antirestriction protein. The R64 ardA gene locating in the leading region of plasmid R64 has been cloned and their sequence has been determined. Antirestriction proteins belonging to the Ard family are specific inhibitors of type I restriction-modification enzymes. The IncI1 ColIb-P9 and R64 are closely related plasmids, and the latter specifies an ArdA homologue that is predicted to be 97.6% (162 residues from 166) identical at the amino acid sequence level with the ColIb = P9 equivalent. However, the R64 ArdA selectively inhibits the restriction activity of EcoKi enzyme leaving significant levels of modification activity under conditions in which restriction was almost completely prevented. The ColIb-P9 ArdA inhibits restriction endonuclease and methyltransferase activities simultaneously. It is hypothesized that the ArdA protein forms two complexes with the type I restriction-modification enzyme (R2M2S): (1) with a specific region in the S subunit involved in contact with the sK site in DNA; and (2) with nonspecific region in the R subunit involved in DNA translocation and degradation by restriction endonuclease. The association of the ColIb-P9 ArdA with the specific region inhibits restriction endonuclease and methyltransferase activities simultaneously, whereas the association of the R64 ArdA with a nonspecific region inhibits only restriction endonuclease activity of the R2M2S enzyme.
可传递质粒IncI1 R64含有编码ArdA抗限制蛋白的ardA基因。位于质粒R64先导区的R64 ardA基因已被克隆并测定了其序列。属于Ard家族的抗限制蛋白是I型限制修饰酶的特异性抑制剂。IncI1 ColIb-P9和R64是密切相关的质粒，后者编码一种ArdA同源物，预计在氨基酸序列水平上与ColIb = P9的对应物有97.6%（166个氨基酸中的162个）相同。然而，R64 ArdA在几乎完全阻止限制作用的条件下，能选择性地抑制EcoKi酶的限制活性，同时保留显著水平的修饰活性。ColIb-P9 ArdA能同时抑制限制性内切酶和甲基转移酶的活性。据推测，ArdA蛋白与I型限制修饰酶（R2M2S）形成两种复合物：（1）与S亚基中与DNA的sK位点接触的特定区域结合；（2）与R亚基中参与DNA转位和被限制性内切酶降解的非特定区域结合。ColIb-P9 ArdA与特定区域的结合同时抑制限制性内切酶和甲基转移酶的活性，而R64 ArdA与非特定区域的结合仅抑制R2M2S酶的限制性内切酶活性。
