Abstract

Endonuclease VII (endo VII) is a Holliday structure-resolving enzyme of bacteriophage T4. Its activity depends on dimerization, DNA binding and hydrolysis of two phosphodiester bonds flanking the Holliday junction. We analysed the DNA-binding activity of truncated monomeric and covalently linked dimeric endo VII proteins. We show that both ends of endo VII are involved in DNA binding. In particular, the C-terminus of one subunit interacts with the N-terminus of the other subunit, constituting one DNA-binding site; the other two termini form the second binding site of the dimer. One binding site is sufficient to bind cruciform DNA. The concerted mechanism involving termini from different subunits ensures that only dimers bind to Holliday structures, thus providing two catalytic centres which introduce two cleavages in opposite strands. This is a precondition for precise resolution of Holliday structures.