The effect of beryllium bonds (BeB) on the tautomerism of 9-methyl-guanine and 1-methylcytosine has been theoretically studied at MP2/aug-cc-pVDZ computational level. It is predicted that BeB will be able to strongly modify the tautomeric behaviour of these nucleobases and, by extension, of DNA and RNA bases. Thus, while the oxo-amino is the most stable tautomer for 9-methyl-guanine and 1-methylcytosine when isolated, they present a relative energy above 33 and 17 kJ mol, respectively, with respect to the most stable tautomer when they form complexes with BeR systems (amino-hydroxy and imino-oxo, respectively). In both cases, the most stable complexes are associated to NBe interactions with binding energies up to 180 kJ mol. ; This work was carried out with financial support from the Ministerio de Economía y Competitividad (Project No. CTQ2015-63997-C2-2-P) and Comunidad Autónoma de Madrid (Project FOTOCARBON, ref S2013/MIT-2841). Computer, storage and other resources from the CTI (CSIC) are gratefully acknowledged. One of us (M.M.-L.) benefits from a contract from the Ministerio de Economía y Competitividad ; Peer Reviewed