FEN structures
The first FEN structure to be solved was by Tom Steitz's group in 1995. It revealed much of the core FEN structure but not all conserved residues were visible. In 1996, within a week of one another, the structures of the T4 RNase H (a FEN despite its name) was reported by Hosfield et al in Cell and we reported a complete structure of T5 FEN in Nature.
Images on the left show the structure of the T5FEN molecule and a close-up of the active site. The crystal structure of T5 FEN Ceska, Sayers, Stier and Suck, Nature 1996. PDB code 1EXN. It contains conserved residues that we have mutated in order to ascertain their role in FEN function. For example see our results published in Nature Structural and Molecular Biology, PNAS Dervan, PNAS Garforth.
Since then, several more FEN structures have been reported, but all share the same structural core. Search the Protein Data Bank for an up to date list using the search term "flap + endonuclease".
The crystal structure of E. coli Exonuclease IX (the xni gene product) were solved in collaborations with Proffessor Pete Artymiuk, now we have observed single stranded DNA threaded through another FEN, from bacteriophage T5 (the T5FEN or D15 5'-3' exonuclease).
Enzyme Product Complex. See Anstey-Gilbert CS et al. It reveals the presence of two very closely spaced Mg ions as well as a potassium ion. Structures with and without DNA were obtained.
See Almalki et al. Shows branched DNA threading through the T5FEN.