Uracil (U) is one of the four nucleotide bases in RNA, with the other three being adenine (A), cytosine (C) and guanine (G). In RNA, uracil pairs with adenine. In a DNA molecule, the nucleotide thymine (T) is used in place of uracil.
Uracil. The fact that uracil is present in RNA and not DNA contributes to the ability of RNA to be degraded easily. This allows the cell to change which genes are being expressed, as the older RNAs do not stick around for very long.
Lawrence Brody, Ph.D.
Division of Genomics and Society