Elsewhere in this volume, 1 it was mentioned that it would be interesting to insert the
targeting motifs of ribotoxins (presumably responsible for the ability to gain access to the
cytoplasm of eukaryotic cells, and the exquisite specificity toward ribosomes) into other
enzyme sequences, in order to generate specific targeted toxins. In this regard, α-sarcin, one
of the most representative ribotoxins, 1 and RNase U2 seem to be the best candidates for
exchange of selected sequence motifs. RNase U2 is a nontoxic extracellular enzyme of the …