Scientists investigating an important DNA-repair enzyme now have
a better picture of the final steps of a process that glues
together, or ligates, the ends of DNA strands to restore the
double helix. The enzyme, DNA ligase, repairs the millions of
DNA breaks generated during the normal course of a cell's life,
for example, linking together the abundant DNA fragments formed
during replication of the genetic material in dividing cells.
"Our study shows that DNA ligase switches from an open, extended
shape to a closed, circular shape as it joins DNA strands
together," says the study's senior author Tom Ellenberger,
D.V.M, Ph.D., the Raymond H. Wittcoff Professor and head of the
Department of Biochemistry and Molecular Biophysics at
Washington University School of Medicine in St. Louis. "The
ligase resembles a wristwatch that latches around the DNA ends
that are being joined." DNA is surprisingly reactive and under
continuous assault from environmental toxins and reactive
cellular metabolites. A means of repairin