A protein called immaturin controlling sexual immaturity in Paramecium

As in many metazoans, clones of some species of Paramecium have, after conjugation, a period of immaturity during which the cells cannot mate. The duration of immaturity is measured by the number of cell generations, which remains fairly constant, although duration in time varies with rate of cell reproduction. Genic involvement is shown by mutants with reduced periods of immaturity. In three different groups of Paramecium species, the cytoplasm of immature cells apparently contains the same substance which represses mating activity when injected into sexually mature cells. The immaturity-inducing substance seems to be absent from sexually mature cells, as brei made not only from mature cells in the stationary phase (mating-reactive cells), but also from those in the log phase (mating-non-reactive cells), does not repress mating activity when injected into mature cells. Variations in the amount of the substance during immaturity suggest that it controls the duration of the period. We have isolated and partially characterized the substance-a single protein called immaturin. The activity of immaturin is dose dependent and associated with a heat-labile protein of molecular weight (MW) 10,000.