Pleiotropic Respiratory-Deficient Mutants

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... 

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-...

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. 

Although the primary deficiency of any yeast chromosomal pleiotropic respiratory strain has not yet been unraveled, these mutants appear to be potentially useful for the biochemical study of membrane biogenesis. They offer new experimental tools in which central processes controlling, directly or indirectly, several mitochondrial activities are specifically affected. 

---