The biosynthesis of a cytotoxic protein, alpha-sarcin, in a mold Aspergillus giganteus. I. Synthesis of prepro- and pro-alpha-sarcin in vitro
Endo, Y.; Oka, T.; Tsurugi, K.; Natori, Y.
Tokushima Journal of Experimental Medicine 40(1-2): 1-6
1993
ISSN/ISBN: 0040-8875 PMID: 8211973 Document Number: 407948
The biosynthesis of alpha-sarcin, a ribosome inactivating protein (16.9 KDa) was studied in a mold Aspergillus giganteus. The fungus begins to secrete alpha-sarcin after reaching a stationary phase around 50 h of culture. The synthesis of alpha-sarcin was shown to be induced at the transcriptional level since the mRNA level of alpha-sarcin, titrated by immuno-precipitation with anti-alpha-sarcin antibodies of translation products in wheat germ cell-free system, was increased synchroniously with the production of the protein. The immuno-precipitates specific for alpha-sarcin contained two species of proteins of 22.5 and 18.5 KDa. The former was localized in the supernatant and the latter was segregated in the microsomes of the wheat germ system. The 22.5 KDa protein was thought to be the primary product of alpha-sarcin, although N-terminal methionine was removed, because it was the only product when the microsomes were solubilized by Triton X-100 prior to translation in the cell-free system. These results indicate that alpha-sarcin is synthesized as 22.5 KDa prepro-alpha-sarcin and is processed cotranslationary into 18.5 KDa pro-alpha-sarcin in endoplasmic reticulum as usual secretary proteins.