Oligodeoxyribonucleotides containing degenerate bases, 6H,8H-3,4-dihyd
ropyrimido[4,5-c] [1,2]oxazin-7-one (P), 2-amino-6-methoxyaminopurine
(K), and N-6-methoxyadenine (Z) were made on a DNA synthesizer. The ol
igonucleotides were used for the preparation of DNA templates by enzym
atic ligation of DNA fragments. The templates were annealed with a pri
mer and extended with Tag DNA polymerase and dNTPs to reveal the nucle
otide(s) incorporated opposite the modified bases. Analysis of the pro
ducts showed that A was inserted opposite the pyrimidine P and T oppos
ite the purines, K and Z. Incorporation of a small amount of C opposit
e K was also observed.