Inhibition of the activity of restriction endonucleases by spermidine and spermine.

Physiological concentrations (0.5-2.0 mM) of spermidine and spermine were observed to inhibit the digestion in vitro of plasmid pJDB 207 by the restriction endonucleases BamHI (EC 3.1.23.6), EcoRI (EC 3.2.23.13), HindIII (EC 3.1.23.20), HpaI (EC 3.1.23.23) and PstI (EC 3.1.23.31). The polyamines protected all the tested restriction sequences of DNA, since the activity of all endonucleases used was strongly inhibited. These results show the need for caution when using polyamines as experimental tools for recombinant DNA chemistry.