This is the
observation that all
introns in
DNA begin with the
nucleotides of "GT" (
guanine,
thymine) and end with the nucleotides "AG" (
adenine,
guanine). When the DNA is
transcribed into
RNA, the introns are removed from the RNA by a mechanism which recognizes these beginning and ending nucleotides - in the RNA they would be "CU" (
cytosine,
uracil) and "AC" (
adenine,
cytosine).
From the BioTech Dictionary at http://biotech.icmb.utexas.edu/. For further information see the BioTech homenode.