The susceptibility of 2,6-diaminopurine (DAP)-containing bacteriophage DNA to several restriction and other endonucleases was examined. With the only exception of TaqI, these enzymes did not accept the modified base as a substitute for adenine. The phage DNA was extensively fragmented by the restriction endonucleases which recognize only G and C-containing sites. 5′-terminal analysis of the MspI and SmaI fragments revealed that d(DAP-T) basepairs can be mistaken by some enzymes for d(G-C) pairs.
