Destruction of immaturin activity in early mature mutants of Paramecium caudatum.

Cells of Paramecium in the sexually immature period of the clonal life cycle contain a protein called immaturin, which represses mating activity when injected into sexually mature cells. The amount of immaturin at various stages of the immaturity period was examined by injecting cytoplasm from immature cells of one wild-type and two early mature mutant clones into mature cells of wild-type. The proportion of immature cells brought about by the injection increased until about 10-15 fissions after conjugation of the donor cells in all three clones. But the percentage of immature cells induced by the injection decreased rapidly from the 25th to the 30th fission of both early mature donors, while the percentage was still high with a wild-type donor of the same fission age. When cytoplasm of the Emt A (early mature mutant) homozygote taken immediately before maturation (about 27 fissions) was injected into the wild-type immature cells of 45 fissions after conjugation, 13% of the recipient cells expressed mating reactivity. But when cytoplasm of Emt A cells 20 and 50 fissions after conjugation was injected into the same cells, no reactive cell appeared. The results suggest that cytoplasm of the early mature mutant immediately before maturation contains some material that accelerates maturation when injected into wild-type cells in the late stage of immaturity. On the other hand, the immature cytoplasm of wild-type cells about 25 fissions after conjugation showed no effect when injected into early mature cells immediately before maturation. The function of the early mature gene product was suggested to be the destruction of immaturin activity.