THE CRYSTAL-STRUCTURE OF FLAP ENDONUCLEASE-1 FROM METHANOCOCCUS-JANNASCHII

Flap endonuclease-1 (FEN-1), a structure specific nuclease, is an esse ntial enzyme for eukaryotic DNA replication and repair. The crystal st ructure of FEN-1 from Methanococcus jannaschii, determined at 2.0 Angs trom resolution, reveals an active site with two metal ions residing o n top of a deep cleft where several conserved acidic residues are clus tered. Near the active site, a long flexible loop comprised of many ba sic and aromatic residues forms a hole large enough to accommodate the DNA substrate. Deletion mutations in this loop significantly decrease d the nuclease activity and specificity of FEN-1, suggesting that the loop is critical for recognition and cleavage of the junction between single and double-stranded regions of flap DNA.