THE INTERACTION OF DNA DUPLEXES CONTAINING 2-AMINOPURINE WITH RESTRICTION ENDONUCLEASES ECORII AND SSOII

Oligonucleotides containing 2-aminopurine (2-AP) in place of G or A in the recognition site of EcoRII (CCT/AGG) or Ssoll (CCNGG) restriction endonucleases have been synthesized in order to investigate the speci fic interaction of DNA with these enzymes. Physicochemical properties (CD spectra and melting behaviour) have shown that DNA duplexes contai ning 2-aminopurine exist largely in a stable B-like form. 2-Aminopurin e base paired with cytidine, however, essentially influences the helix structure. The presence of a 2-AP . C mismatch strongly reduces the s tability of the duplexes in comparison with the natural double strand, indicated by a biphasic melting behaviour. Ssoll restriction endonucl ease recognizes and cleaves the modified substrate with a 2-AP . T mis match in the centre of the recognition site, but it does not cleave th e duplexes containing 2-aminopurine in place of inner and outer G, or both. EcoRII restriction endonuclease does not cleave duplexes contain ing 2-aminopurine at all. The two-substrate mechanism of EcoRII-DNA in teraction, however, allows hydrolysis of the duplex containing 2-amino purine in place of adenine in the presence of the canonical substrate.