Oligonucleotide duplexes containing inosine, 7-deazainosine, tubercidin, nebularine and 7-deazanebularine as substrates for restriction endonucleases HindII, SalI and TaqI.

Synthetic hexadecanucleotide duplexes containing a single purine nucleotide analogue in the recognition sites of the restriction endonucleases HindII, SalI and TaqI were used to investigate the restriction site determinants required by these enzymes for sequence recognition and phosphodiester bond cleavage. The enzymes were, in general, unaffected by changes introduced into the minor groove of the helix. SalI was found to be inhibited by the major groove modifications introduced into the fourth position of its recognition sequence GTCGAC. HindII and TaqI were, by contrast, able to cleave the sites containing the analogues at this position. TaqI and, to a lesser extent, HindII could also be shown to tolerate "mismatch analogues" at this site.