Biology Reference
In-Depth Information
5'-GG3' sites in the complementary strand were employed in this
study. Single base mismatches were introduced between the two
guanine doublet steps, and the e
ciency of charge transport
through the mismatches was determined through measurements of
the ratio of oxidative damage at the guanine doublets distal versus
proximal to the intercalated ruthenium oxidant. The damage ratio
of oxidation at the distal versus proximal site for the duplexes
containing different mismatches varied in the following order GC
∼
∼
∼
>
>
∼
∼
∼
CT. The authors
suggested that that this ordering may be ascribed in part to local
changes in helical stability. However, these changes cannot be easily
explained through an increased solvent accessibility associated
with a mismatch. Marques
et al.
[36] demonstrated methodology
based on perturbation of the double helix
π
-stack introduced
by a mismatched nucleotide. In this investigation CYP3A4*1B
oligonucleotideswereimmobilizedonthesurfaceofagoldelectrode
andhybridizedwithfullycomplementaryoligonucleotidesequences
as well as with mismatched sequences corresponding to the
CYP3A4*1A reference sequence. The methodology developed could
identify CYP3A4*1A homozygotes by the 5
μ
C charge attenuation
observedwhencomparedwithDNAsamplescontainingatleastone
CYP3A4*1Ballele.Inanotherinvestigation,Boal
et al.
[37]employed
the DNA-modified gold electrodes to monitor the electrocatalytic
reduction of DNA-bound methylene blue for a wide range of
base analogues and DNA damage products. It was found that
the e
ciency of DNA-mediated charge transfer is independent of
the thermodynamic stability of the helix. However, modifications
to the hydrogen bonding interface in a given Watson-Crick base
pair and added steric bulk yielded a substantial loss in charge
transfer e
ciency. Base structure modifications that induce base
conformational changes and those that bury hydrophilic groups
within the DNA helix also appeared to attenuate charge transfer
in DNA. Addition and subtraction of methyl groups that do not
interferewiththeH-bondinginteractionsofthebasesdidnotappear
to have any significant effect on the CT e
ciency. Importantly, the
system was capable of detecting base pair mismatches and base
damage products. Inouye
et al.
[38] reported an electrochemical
DNA sensor for the detection of single-nucleotide polymorphism.
GG
GT
GA
AA
CC
TT
CA
