Secretion of an Mr 60000 protein by benomyl-treated cells of Neurospora crassa.

In the presence of the microtubule inhibitor benomyl at micron concentrations, cells of Neurospora crassa wild type strain St. Lawrence 74A were found to secrete high amounts of an Mr 60 000 protein into the culture medium (about 35 micrograms/ml after a 12 h treatment). The secretion also occurred after treatment with the other antitubulin drugs carbendazim (MBC), nocodazole, thiabendazole, and griseofulvin. This secretion is apparently induced by the specific action of benomyl on N. crassa beta-tubulin as no secretion of the Mr 60 000 protein could be detected after treatment of the benomyl-resistant mutant bml 511 (r), mutated in its beta-tubulin gene (Orbach et al., Mol. Cell. Biol. 6, 2452-2461 (1986)). The secretion was abolished by 12 microM cycloheximide, a protein synthesis inhibitor. The Mr 60 000 protein could be separated into two main and four secondary components by two-dimensional gel electrophoresis (pI 6.67 and 6.52 and pI 6.93, 6.81, 6.44, and 6.32, respectively). The Mr 60 000 protein was not a major intracellular protein of benomyl-treated cells and could only be revealed by immunoblotting with polyclonal antibodies raised against the extracellular form. It was undetectable in untreated cells collected at various stages of vegetative growth or in their culture medium.