Uracil is one of the four nitrogenous bases found in RNA (ribonucleic acid), the other three being adenine, guanine, and cytosine. Uracil pairs with adenine in RNA, just as thymine pairs with adenine in DNA. RNA is a single-stranded molecule that plays a crucial role in protein synthesis and gene expression. The presence of uracil in RNA is what distinguishes it from DNA, which contains thymine instead.