5-STRANDED BETA-SHEET SANDWICHED WITH 2 ALPHA-HELICES - A STRUCTURAL LINK BETWEEN RESTRICTION ENDONUCLEASES ECORI AND ECORV

Examination of crystal structures of restriction endonucleases EcoRI a nd EcoRV complexes with their cognate DNA revealed a common structural element, which forms the core of both proteins, This element consists of a five-stranded beta-sheet and two alpha-helices packed against it and could be described as alpha-beta sandwich in which helices and be ta-strands lie in two stacked layers, While the spatial structure of t his alpha-beta sandwich is conserved in both enzymes, there are no det ectable similarities between amino acid sequences except of a few resi dues involved in active site formation, Probably, other restriction en donucleases which have similar organization of the active site might p ossess similar structural element regardless of DNA sequence recognize d and recognition elements in the enzyme used. (C) 1994 Wiley-Liss, In c.