[Biochemical characteristics of new thermosensitive secretory mutants of yeasts].

New thermosensitive mutants of the yeast Saccharomyces cerevisiae which block the secretion of periplasmic enzymes at restriction temperature have been obtained. These mutants accumulate active low molecular weight and mature invertase species in the cell; the buoyant density of the cells in a Percoll gradient is higher than that in the wild strain cells. The mutant cells transferred to permissive temperature (25 degrees C) in the absence of protein synthesis can secrete some amount of accumulated invertase. It was found that the secretory defects of conditional mutants do not affect the activity of cytoplasmic enzymes (e.g., alcohol dehydrogenase) or the level of total protein synthesis and glycosylation and do not induce non-specific disturbances in energy metabolism and plasma membrane functions at restriction temperature. Some strains of new secretory mutants revealed uncoupled defective secretion of periplasmic enzymes and intrinsic membrane proteins (proline permease). The possibility of branching of the secretory pathway for periplasmic enzymes and cytoplasmic membrane proteins is discussed.