POLYNUCLEOTIDE-ADENOSINE GLYCOSIDASE ACTIVITY OF SAPORIN-L1 - EFFECT ON DNA, RNA AND POLY(A)

The ribosome-inactivating proteins (RIPs) are a family of plant enzyme s for which a unique activity has been determined: rRNA N-glycosidase, which removes adenine at a specific universally conserved position (A (4324) in the case of rat ribosomes). Here we report that saporin-L1, a RIP from the leaves of Saponaria of officinalis, recognizes other su bstrates, including RNAs from different sources, DNA and poly(A). Sapo rin-L1 depurinated DNA extensively and released adenine from all adeni ne-containing polynucleotides tested. Adenine was the only base releas ed from DNA or artificial polynucleotides. The characteristics of the reactions catalysed by saporin-L1 have been determined: optimal pH and temperature, ionic requirements, and the kinetic parameters K-m and k (cat). The reaction proceeded without cofactors, at low ionic strength , in the absence of Mg2+ and K+. Saporin-L1 had no activity towards va rious adenine-containing non-polynucleotide compounds (cytokinins, cof actors, nucleotides). This plant protein may now be classified as a po lynucleotide :adenosine glycosidase.