Special topic: Metagenomics - Genome Sciences

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Living with UV-damage: Photolyases & UVDE
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less stable than native polymerase–DNA
complexes22 . Nucleotide substrates diffused
out of the CPD-containing complexes during
equilibration of the crystals before freezing.
The resulting structures show an open
conformation of the fingers, similar to that
of unliganded T7 DNA polymerase (data not
shown). To overcome the low affinity for
nucleotide substrates in the CPD complexes,
we added nucleotides to the cryopreservation
buffers used for harvesting the crystals.
Three different CPD-3! structures were
determined using crystals equilibrated in
0 mM, 1 mM or 10 mM ddATP in the
harvesting solutions and they are named
CPD-3!a, CPD-3!b, and CPD-3!c, respectively.
Two structures of CPD-5! complexes
were determined with 0 mM or 10 mM
ddATP added (the CPD-5!a and CPD-5!b
complexes; Table 1). All of the structures
were determined by molecular replacement
Photoreactivation is a repair system specific for dealing with pyrimidine dimers.
Photolyase enzymes contain a FADH2 group that absorbs light between 350-500 nm,
and catalyze separation of fused bases.
using a model of T7 DNA polymerase 22 . The
structures have been refined to resolution
limits ranging from 2.2 to 2.3 Å, except for
the CPD-3!c complex, which has a resolution
limit of 3.2 Å (Table 2 and Figs. 1 and 2).
Figure 2 A cis-syn thymine dimer and electron density maps around its binding sit
structures. (a) Schematic drawing of a cis-syn thymine dimer. (b) CPD-3!a complex
nucleotide in the harvesting solutions showing the electron density for the CPD out
polymerase active site. (c) CPD-3!c complex with 10 mM incoming nucleotide in th