cau 4 :

- cac enzyme co kha nangf han che su fat trien cua cac phage trong te bao VK bang cach fan huy ADN of phage 1 cach dac hieu goi la enzyme cat gioi han.

- 1970 Halmilton Smith  tach dc RE dau tiern tu VK Haemophilus Influenzae chung Rd dc goi la hind II

** DAC diem va TJnh chat :

- ENzyme cat gioi han phan huy bat ki ADN ngoai lai nao xam nhap vao tb VK . De ngan ngua enzyme nay tac dong vao ADN vat chu bang cach metyl hoa cac base xac dinh trong trinh tu nhan biet nho vay ngan can RE cat vao ADN cua tb vat chu .

- RE co dac tinh k cat ADN k dac hieu loai : nghia la RE tach chiet tu VK con cat ADN trong tb DV, TV,VK o cung vi tri gioi han hoac dac diem gioi han. So luong kich thuoc ngan dai tuy thuoc vao so luong diem gioi han tren fan tu ADN.

- RE co 3 kieu I, II, III. Cac enxzyme dc dung fo bien thuoc kieu II, co che tac dung don gian . Chung la cac nuclease vi chung cat tai 1 vi tri nam ben trong soi ADN nen goi la cac endoniuclease.

- CAc RE nhan biet ADN mach kep o nhung trinh tu diem nhan biet va cat ADN o ngay diem nay hoac diem ke can. Cac trinh tu nhan biet thuong co cap tu 4-6 cap nu doi khi co toi 8 cap nu.

- MOi enzyme gioi han nhan biet va cat dac hieu 1 doan ADN o nhung vi tri nhat dinh . CO 2 kieu cat khac nhau la cat tao dau bang cach va cat tao dau lech co ket con goi la dau dinh.

** VAi tro' : Neu vi tri cat RE o giua trinh tu nhan biet thj tao nen chuoi ADN dau bang mcac dau bang bi cat cua fan tu ADN k co kha nang tu ket hop lai vs nhau > De noi cac doan ADN vs nhau can su dung enzyme noi - ADN ligase hoac doan noi ( linker ) hoac cac adapter chuyen dung cho mmoi loai enzyme . Neu vi tri cat nam canh trinh tu nhan biet thi tao ra dau sole . Cac dau sole tao vien saukhi cat co the tu noi lai vs nhau k can co mat enzyme noi. Nhjo dac tinh nay enzyme gioi han cat tac cac doanADNcac dau sole dc dung nhieu trong ki thuat ADN tai to hop.

- Cac fan tu ADN khacnhau dc cat boi cung 1 loai enzyme gioi han hoac kha nang ket hop ket hop vs nhau tao nen ftu ADN  tai to hop wa cac dau dinh . CAc doan ADN dc tao nen nho hoat tinh cat tao dau dinh cua enzyme gioi han co the tiu noi lai vs nhau hoac noi vs nhung doan ADN co cac dau tuong tu nen dc use rat nhieu trong ADN tai to hop. => hien nay co khoang 3000 RE . Cac RE su dung nhieu  : ENco RI, Eco RV, Bam HI, SmaI