Na. Gormley et al., Reactions of BglI and other type II restriction endonucleases with discontinuous recognition sites, J BIOL CHEM, 275(10), 2000, pp. 6928-6936
Type II restriction enzymes generally recognize continuous sequences of 4-8
consecutive base pairs on DNA, but some recognize discontinuous sites wher
e the specified sequence is interrupted by a defined length of nonspecific
DNA. To date, a mechanism has been established for only one type II endonuc
lease with a discontinuous site, SfiI at GGCCNNNNNGGCC (where N is any base
). In contrast to orthodox. enzymes such as EcoRV, dimeric proteins that ac
t at a single site, SfiI is a tetramer that interacts with two sites before
cleaving DNA. BglI has a similar recognition sequence (GCCNNNNNGGC) to Sfi
I but a crystal structure like EcoRV. BglI and several other endonucleases
with discontinuous sites were examined to see if they need two sites for th
eir DNA cleavage reactions. The enzymes included some with sites containing
lengthy segments of nonspecific DNA, such as XcmI (CCANNNNNNNNNTGG). In al
l cases, they acted at individual sites. Elongated recognition sites do not
necessitate unusual reaction mechanisms. Other experiments on BglI showed
that it bound to and cleaved DNA in the same manner as EcoRV, thus further
delineating a distinct group of restriction enzymes with similar structures
and a common reaction mechanism.