Mutants respiratory deficient, 5. cerevisiae

Two bursts in the production of acid-soluble PolyPs were shown to occur during the growth of some S. cerevisiae strains on a medium containing glucose and galactose under aerobic conditions (Solimene et al., 1980). The respiratory deficient mutant, however, had only one PolyP burst , which indicated that the accumulation of PolyP produced in the first burst depended on the active mitochondrial function (Solimene et al., 1980). 

Coxl7, an 8.1-kDa cysteine-rich protein, was the first copper chaperone to be identified. Saccharomyces cerevisiae harboring mutations in coxl 7 are respiratory deficient, a phenotype resulting from their inability to assemble a functional cytochrome c oxidase complex (Glerum et al., 1996a). coxl7 mutant yeast are, however, able to express all the subunits of the cytochrome c oxidase complex, indicating that the lesion must lie in a posttranslational step that is essential for assembly of the functional complex in the mitochondrial membrane. Unlike other cytochrome c... 

S. cerevisiae is studied in regard to the biochemical regulation of malic acid production (Pines et al., 1996). Under environmentally stressed conditions, a small amoxmt of fumaric acid and malic acid (less than lOg/L) was produced by this common yeast. Similar to the malic acid production pathway of Aspergillus, the cytosolic reductive pathway of acid synthesis and accumulation has been shown in S. cerevisiae. A NMR study involving glucose conversions to malic acid indicates that the following reactions lead to malic acid accumulation pyruvate oxaloacetate->fumarate malate. The involvement of cytosolic fumarase in the conversion of fumaric acid to malic acid has been corroborated. Wang et al. (1988) have shown the ability of a cytoplasmic respiratory deficient mutant of S. cerevisiae to convert fumarate to malate without the participation of mitochondrial fumarase. 

When dealing with pleiotropic respiratory-deficient mutants of yeast, three practical difficulties constantly arise. The major inconvenience is the general genetic instability of the chromosomal pleiotropic respiratory-deficient mutants in S. cerevisiae where an additional p mutation spontaneously arises with very high frequency Since both the nuclear and the mitochondrial mutations are often expressed by deficient cytochromes aas and b, as well as by the loss of oligomycin sensitivity of the ATPase, the biochemical study of these double mutants is very difficult. An easy way out of this difficulty is to use chromosomal respiratory-deficient mutants of a petite-negative yeast species like 5. pombe, where no viable p mutation can be induced. 

Chromosomal pleiotropic respiratory-deficient yeast mutants with multiple cytochrome deficiencies were first described by Sherman and SlonimskP in S, cerevisiae. Several combinations of cytochromes aa, b, c, and Cl deficiencies have been described more recently. The most common pleiotropic cytochrome deficiencies in S. cerevisiae concern both cytochromes aaz and b (strains pi, p6, p7 of ref. 85, strain plO of ref. 91, and strains S5, S6, S7, S9, S13, S19, and S20 of ref. 92). Strains 8, 16, 25, 486, 881, and El of ref. 93 might also be classified in the same class, although an additional deficiency in cytochrome Ci was reported. 

As noted above, all S. cerevisiae pleiotropic mutants described so far produce secondary p mutations at very high rates. This problem is easily solved by the use of S. pombe, where several distinct classes of chromosomal pleiotropic respiratory-deficient mutants have been described to date (Table V). Curiously, all pleiotropic strains of S. pombe reported so far are deficient in cytochrome aa and/or cytochrome oxidase. Early reports of additional deficiencies of the respiratory chain were hardly quantitative because of the poor basic knowledge of the respiratory chain in S. pombe and imperfect control of the interference produced by glucose repression. More recent papers report deficiencies in a cytochrome 561.5.Two types of ATPase deficiencies were also reported (a) the total absence or presence in reduced amount, of Dio-9-sensitive ATPase, and (b) the oligomycin-insensitive ATPase. 

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