They then treated the nuclei with a chemical that converts cytosines without methyl groups to the RNA base uracil. (scientificamerican.com)
The radiation and harsh temperatures broke down pyrimidine in the ice and formed new compounds related to life, such as uracil and cytosine. (discovermagazine.com)
The first three are the same as those found in DNA, but in RNA thymine is replaced by uracil as the base complementary to adenine. (sciencedaily.com)