DNA‐nuclease activity of the single‐chain ribosome‐inactivating proteins dianthin 30, saporin 6 and gelonin

The single-chain ribosome-inactivating proteins (scRIPs) from plant origin are antiviral and antiproliferative agents employed in the preparation of immunotoxins. Similarly to the A-chains of ricin, sc-RIPs act as rRNA N-glycosidases. We demonstrate here that dianthin 30, saporin 6 and gelonin exert a specific nuclease activity on supercoiled DNA. Four specific sites of cleavage introduced by dianthin 30 and by saporin 6 and two specific sites of cleavage introduced by gelonin have been identified and mapped in pBR322.