Bend, Fray, Cut: A Unified Mechanism for Exo- and Endo-Nucleases

Two related manuscripts appear in the April 15 issue of CELL reporting results endo and exo nucleases important for DNA repair. Both groups of researchers made extensive use of the MX capabilities of the SIBYLS beamline to collect critical crystallographic data. The crystal structures of human flap endonuclease (FEN1) in complex with both substrate and product forms of DNA were reported by Susan Tsutakawa *et al*. in the following manuscript:

Published simultaneously by Jill Orans *et al* is the crystal structure of human exonuclease 1 in complex with DNA substrate.

Together these two manuscripts present exciting insights into the molecular principles governing diverse endo- and exonucleolytic cleavage specificities of members of the RAD2/FEN superfamily of nucleases, which have critical roles in DNA replication and maintenance.