Title: DNA Bases beyond Watson and Crick T. Carell, Center for Integrative Protein Science at the Department of Chemistry, Ludwig Maximilians University, Munich, Butenandtstr. 5-13, 81377; e-mail: firstname.lastname@example.org; www.carellgroup.de Keywords: Epigenetics, oxidized pyrimidine bases, mass spectrometry, proteomics. Abstract: Epigenetic information is stored in the form of modified bases in the genome. The positions and the kind of the base modifications determines the identity of the corresponding cell. Setting and erasing of epigenetic imprints controls the complete development process starting from an omnipotent stem cells and ending with an adult specialized cell. I am going to discuss results related to the function and distribution of the new epigenetic bases 5-hydroxymethylcytosine (hmC), 5-formylcytosine (fC), 5-carboxycytosine (caC) and 5-hydroxymethyluracil (Scheme 1). These nucleobases seem to control epigenetic programming of cells and establish genetic programmability. Synthetic routes to these new bases will be discussed that enable the preparation of oligonucleotides. The second part of the lecture will cover mass spectroscopic approaches to decipher the biological functions of the new bases. In particular, results from quantitative mass spectrometry, new covalent-capture proteomics mass spectrometry and isotope tracing techniques will be reported. Finally I am dicussing potential präbiotic origins of modified bases.