Restrictive phenotype of sec 7 mutant of Saccharomyces cerevisiae was examined by freezefracture electron microscopy. In accordance with previous findings (NOVICK et al. 1981) dictyosomes and middle-size (200-600 nm) vesicles (Berkeley bodies) were found to accumulate. Dictyosomes are formed by aggregated flattened or dilated cisternae without associated secretory vesicles. After transfer to permissive conditions the dictyosomes disappear and are not detectable, just like in the wild type or in the permissive phenotype. Associated with the restrictive phenotype is an extended plasma membrane and tonoplasts with particle-free impressions.

Department of Biology Medical Faculty J E Purkynĕ University Brno Czechoslovakia

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