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Fig. 11. Model of the cytotoxic internalization of ribonucleases. RNase A and ONC
bind to the cell surface and are internalized by dynamin-independent
endocytosis. Like diptheria toxin, both ribonucleases probably reach the
cytosol by translocation from an endosome. Unlike diphtheria toxin, the low pH
of acidic endosomes is not a prerequisite for the translocation of RNase A and
ONC to the cytosol. The entry of ONC to the Golgi is inefficient for
cytotoxicity. Unlike ricin and Shiga toxin, both ribonucleases reach the
cytosol by translocation from a pre-ER compartment.