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Methods and Materials
THEORY OF DGGE
DGGE is a technique that separates DNA fragments of the same length but
with different guanine + cytosine (G+C) base content. Separation is based
on the concentration of a denaturant such as urea or formamide needed
to effect separation (melting) of double-stranded helical fragments into
partially-separated, single-stranded fragments. The G+C content of the
fragment determines the denaturant concentration at which domains of the
fragment will melt. A partially-melted fragment migrates more slowly through
a polyacrylamide gel than does an undegraded, helical, doublestranded
DNA molecule. The denaturation reaction can be controlled by establishing
a gradient of DNA denaturants such as urea and formamide within the gel.
During electrophoresis, the migrating double-stranded fragment begins
to melt upon exposure of various domains of the fragment to an increasing
denaturant concentration. Domains with a low %G+C will melt at a low denaturant
concentration, while domains with high %G+C melt at higher denaturant
concentrations further down the gel.
A 40 base pair (bp), GC-rich oligonucleotide referred to as a GC-clamp
can be attached to the fragments using cloning techniques to retard migration
of melted fragments through the gel to achieve better resolution of fragments
with small differences in sequence variati
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