Cytosine homo base pairs

The binding of a variety of deoxyribo- and ribo-, homo- and copolynucleotide complementary duplexes to agarose-linked homopolynucleotides has been evaluated, to determine the specificity of recognition of complementary base pairs in triple helix formation under physiological conditions.332 The full range of conceivable base triplets was studied, to determine which triplets can and cannot form - i.e. to establish a third strand binding code. Besides the requirements for a cluster of purine bases in one strand, and for third-strand cytosine bases to be protonated, the allowable base triplets were found to be A.A.T/U U.A.T/U G.G.C C+G.C I.A.T/U and I.G.C. 

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