THE MODE OF ACTION OF HIRSUTELLIN-A ON EUKARYOTIC CELLS

A 16-kDa protein toxin was purified from Hirsutella thompsonii var tho mpsonii and named hirsutellin A (HtA). At 0.5 and 5.0 mu M concentrati ons, HtA caused detectable cytopathic effects on Spodoptera frugiperda cells (Sf-9) within 2-4 hr and completely inhibited Sf-9 cell growth at 4 days posttreatment. Electron microscope data showed that the HtA treated Sf-9 cells became hypotrophied and internal organelles and cel l membranes were disrupted. At the same concentration, HtA effectively inhibited Brome mosaic virus protein synthesis of both rabbit reticul ocyte and wheat germ in vitro translation systems. The ribosomal RNA e xtracted from HtA treated Sf-9 cells produced a smaller RNA (approxima tely 528 bases) than untreated Sf-9 cells. In summary, HtA is the firs t mycotoxin of a invertebrate mycopathogen determined to possess ribos omal inhibiting activity and appears to possess some specificity to in vertebrate cells. (C) 1996 Academic Press, Inc.