Consequences of the overexpression of ubiquitin in yeast: elevated tolerances of osmostress, ethanol and canavanine, yet reduced tolerances of cadmium, arsenite and paromomycin.

Ubiquitin is induced by diverse stresses in all eukaroytes probably in reflection of the need for more extensive protein turnover by the ubiquitination system in stressed cells. To determine if ubiquitin overexpression can confer general protection against different stresses, yeast cells were engineered to overexpress ubiquitin and the effects of this overexpression on different stress tolerances determined. Ethanol and osmostress tolerances were slightly increased by ubiquitin overexpression, tolerance to heat was unaffected, while still other tolerances were reduced as compared to cells with normal ubiquitin levels. It is noteworthy that tolerance of the amino acid analogue canavanine was markedly increased by ubiquitin overexpression, yet resistance to at least three other agents that contribute to accumulation of aberrant proteins (arsenite, cadmium, paromomycin) was decreased.