Temperature-sensitive mutants of Dictyostelium discoideum.

Three classes of temperature-sensitive mutants of the cellular slime mold Dictyostelium discoideum have been isolated. One class contains strains able to grow at 22 C but not at 27 C. Cells of these strains can develop into sorocarps at both temperatures. Another class contains strains which can grow at both temperatures but can only develop at the lower temperature. The third class contains strains unable to grow or develop at 27 C. Those strains whose development is temperature-sensitive appear to carry mutations which affect the cells only during the period of aggregation before the construction of a multicellular sorocarp. When pairs of growth-temperature-sensitive (GTS) strains develop in mixed aggregates, temperature-resistant (TR) cells are formed at a frequency of about 10(-4). These TR cells transmit the phenotype in a relatively stable hereditary fashion. However, temperature-sensitive segregants can be isolated from TR strains even after six clonal passages. Mixed incubation of pairs of morphologically aberrant GTS strains was found to give rise to TR progeny which develop normally. These progeny clones independently segregate morphologically aberrant strains and temperature-sensitive strains. The results indicate that several temperature-sensitive and morphological mutations are recessive and nonidentical.