The ribosomes of Aspergillus giganteus are sensitive to the cytotoxic action of α-sarcin

Ribosomes in lysates prepared from the mycelia of Aspergillus giganteus MDH 18894, which are actively secreting α-sarcin, do not contain the α-sarcin lesion. However, the addition of exogenous α-sarcin to these same lysates results in cleavage of the 26 S rRNA of the 60 S ribosomal subunit, characteristic of the cytotoxic action of α-sarcin. We conclude that A. giganteus ribosomes are not inherently resistant to the action of α-sarcin but are protected in vivo by producing α-sarcin in an inactive form and/or by the efficient cotranslational secretion of the toxin.