Respiratory deficient mutants

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). 

Bernardi G., Faures M., Piperno G., Slonimski P.P. (1970). Mitochondrial DNA s from respiratory-sufficient and cytoplasmic respiratory-deficient mutant yeast. J. Mol. Biol. 48 23-42. 

Respiratory-deficient mutant forms of brewing yeast arise from time to time. Because they produce a different balance of metabolic products than the parent strain, they tend to influence the flavour of the beer. For instance they may produce unacceptable levels of vicinal diketones, notably diacetyl. They arise spontaneously but may be induced by a variety of substances, including copper salts [97] and formaldehyde [98]. 

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. 

Stable Pleiotropic Respiratory-Deficient Mutants of a Petite-Negative Yeast... 

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. 

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. 

Isolation and Frequency of Pleiotropic Respiratory-Deficient Mutants in Schizosaccharomyces pombe... 

All respiratory-deficient mutants described so far are derived directly or indirectly from the well-characterized strain, Schizosaccharomyces... 

Properties of the Chromosomal Pleiotropic Respiratory-Deficient Mutant, Ml26... 

Primary Deficiencies in Pleiotropic Respiratory-Deficient Mutants... 

Table VII. Some Possibilities for the Function of the pet Gene Product Primarily Modified in the Chromosomal Pleiotropic Respiratory-Deficient Mutant Schizo-...

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