The exchange of RNA and protein during conjugation in Tetrahymena.

SYNOPSIS. Exchange of cytoplasm in Tetrahymena pyriformis, syngen 1, has been demonstrated by growing cells of 1 mating type in medium supplemented with H3-uridine or H3-histidine, washing, mixing with cells of an unlabeled, starved mating type, sampling conjugants at different times, and preparing autoradiographs. It was found that cytoplasmic interchange begins soon after the mates unite, and has become extensive before the end of the 1st prezygotic prophase (micronuclear crescent stage). When the RNA in one mating type had been labeled with H3-uridine, the activity was distributed almost evenly between the mates by late stages of conjugation. These results are consistent with electron micrographs of this syngen showing small pores in the attachment region of the mates, and many free ribosomes in the cytoplasm (8,11). By contrast, when protein in one mating type had been labeled with H3-histidine, these cells at late conjugation remained about twice as active as their originally unlabeled mates, presumably because of the physical characteristics of some structures which incorporated the amino acid (for example, cilia and membranes of the cell surface; cytoplasmic bodies, such as mitochondria, larger than the pores). That the radioactivity in the originally unlabeled cells came from their mates and not from the environment is indicated by the continued presence of inactive non-conjugants after 1 and 2 days in the mating type mixtures. Other cells which did acquire small amounts of active cytoplasm probably had engaged in abortive conjugation, separating from labeled mates before forming and exchanging pronuclei.