A Third Strand for DNA
from chemistry world
The DNA double helix can under certain conditions accommodate a third strand in its major groove. Researchers in the UK have now presented a complete set of four variant nucleotides that makes it possible to use this phenomenon in gene regulation and mutagenesis.
Natural DNA only forms a triplex if the targeted strand is rich in purines - guanine (G) and adenine (A) - which in addition to the bonds of the Watson-Crick base pairing can form two further hydrogen bonds, and the 'third strand' oligonucleotide has the matching sequence of pyrimidines - cytosine (C) and thymine (T). Any Cs or Ts in the target strand of the duplex will only bind very weakly, as they contribute just one hydrogen bond. Moreover, the recognition of G requires the C in the probe strand to be protonated, so triplex formation will only work at low pH.
from chemistry world
The DNA double helix can under certain conditions accommodate a third strand in its major groove. Researchers in the UK have now presented a complete set of four variant nucleotides that makes it possible to use this phenomenon in gene regulation and mutagenesis.
Natural DNA only forms a triplex if the targeted strand is rich in purines - guanine (G) and adenine (A) - which in addition to the bonds of the Watson-Crick base pairing can form two further hydrogen bonds, and the 'third strand' oligonucleotide has the matching sequence of pyrimidines - cytosine (C) and thymine (T). Any Cs or Ts in the target strand of the duplex will only bind very weakly, as they contribute just one hydrogen bond. Moreover, the recognition of G requires the C in the probe strand to be protonated, so triplex formation will only work at low pH.
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