The Genotypic Control of Kappa in Paramecium Aurelia, Syngen 4, Stock 51.

HE killer trait in all stocks of Paramecium aurelia which have been investiTgated has been found to depend upon the presence of a cytoplasmic factor, kappa, carried by killers but absent from sensitive animals (SONNEBORN 1943). Kappa is a DNA containing particle of about one micron in size (PREER 1950a; PREER and STARK 1953). When kappa disappears from the cytoplasm of a killer, the animal loses the ability to produce P particles (responsible for the killing action) and at the same time becomes sensitive to them (SONNEBORN 1946; PREER 1948). The understanding of the relation of kappa to the nuclear genes of Paramecium has undergone changes with increasing knowledge and is further modified by the results to be presented in this paper. SONNEBORN (1943) early demonstrated the presence of a pair of alleles, K and k, which play a decisive role in the control of the maintenance of kappa particles. Under standard conditions of culture, kappa and the killer trait are maintained by animals of genotype KK and Kk, but they are lost by animals of genotype kk. When this was the only known locus related to the maintenance of kappa, the possibility of an intimate and direct relation between the allele K and kappa was entertained ( SONNEBORN 1945). This possibility, first rejected on other grounds (SONNEBORN 1946), was soon rendered untenable by the discovery of a second locus (S-s) affecting the maintenance of kappa ( SONNEBORN 1947b). Animals of genotype KK SS give rise to a “mixed” clone, that is a clone characterized by the presence of sensitive as well as killer lines of descent. Since the sensitives are killed by the action of P particles secreted by the killer animals, mixed clones are characterized by the occurrence within them of a specific type of autolethality. A clone of genotype KK ss behaves as a pure killer and produces no sensitives under standard conditions of culture. Mixed clones were obtained following crosses between the killer stock 51 and either of the sensitive stocks 29 or 32 in syngen 4 of Paramecium aurelia. Stock 51 carries the allele s, stock 29-and presumably stock 32-carry the allele S. As will appear, two such S-s loci have now been found and more are suspected of existing.