Negative complementation among ad ₂mutants of yeast

Summary

Ad ₂ remedial mutants of Saccharomyces cerevisiae which showed conditional growth at 35°C or with 1 M KCl at 25° C or 35° C, were crossed with other remedial and non-remedial mutants in all pairwise combinations. 19 remedials (11 K ₂₅, 5 temp. and 3 K ₃₅) and 189 non-remedial mutants were used. The standard conditions used were incubation at 25° C in the absence of adenine.

Among 1625 combinations there were 367 (22.6%) cases of negative complementation. In these cases the diploids were unable to grow under the same conditions which permitted a strong growth of the remedial haploid.

No negative complementation was observed among K ₂₅×K ₂₅ combinations. When only one haploid partner was remedial the temp. ¢ non-remedial combinations showed a rate 2.5 times higher than that observed among K ₂₅ × non-remedial combinations. When the remedial haploid was a K ₃₅ the incidence was the same as that noted with temp. × non-remedial combinations. The high incidence observed in the latter temp. combinations was not subject to influence attributable to strain; the incidence being the same whether the remedial partner belonged to the a or to the α mutant strains. The K ₂₅ × non-remedial combinations, on the other hand, showed such an influence.

For an explanation of the mechanism involved in negative complementation it was postulated that, assuming non-random monomer aggregation, some mutant pairs would form only active heterologous multimers while others, due to the nature of their mutation, would form only inactive aggregates which entrap all the remedial monomers. It is thought that this postulate may have some application in explaning the complementation mechanism in general.