2',5'-DNA CONTAINING GUANINE AND CYTOSINE FORMS STABLE DUPLEXES

2',5'-Linked DNA oligomers bearing the bases guanine and cytosine are found to associate. Three 2',5'-DNA strands composed entirely of the b ases guanine and cytosine, two mutually complementary dodecamers, and a self-complementary octamer were prepared. Melting temperatures and f ree energies of duplex formation were determined for these oligomers a nd their natural, 3',5'-linked DNA counterparts. From these data it wa s seen that 2',5'-DNA duplexes have free energies approximately half t hat of the corresponding natural DNA duplexes under high ionic strengt h conditions (1 M NaCl). 2',5'-DNA strand association was also found t o persist under conditions of low solution ionic strength. These obser vations are consistent with 2',5'-linked DNA comprising an alternative genetic material. A model is proposed where present-day 3',5'-linked nucleotides arose by ''genetic takeover'' of 2',5'-linked nucleotides.