guanine By Ivan Suarez Robles 07 Feb, 2011 One of the four nitrogenous bases found in DNA; pairs with the base cytosine; often abbreviated as the letter ‘G’; see Figure B-3.Related Articles: NPR's This American LifeGlossary: mismatch repair enzymeGlossary: mithramycinAll About MutationsAn Introduction to DNA and Chromosomes (Text and Audio)