EcoRII was the first restriction endonuclease (ENase) reported requiri
ng the cooperative interaction with at least two DNA sites for activit
y. Using two different expression systems the enzyme could be purified
and its special substrate requirements were further analyzed. At the
present state of knowledge we suggest a model of simultaneous binding
of two DNA sites to one dimeric enzyme molecule (see Kruger et al., FE
MS Microbiol. Rev. (1995) in press).