Limiting conditions for conjugation in Tetrahymena: Cellular development and factor active in conjugation

Abstract

AbstractConjugation in Tetrahymena thermophila is a three component system requiring starved cells of two complementary mating types and an extracellular macromolecular factor active in conjugation (FAC). Because the rate of cell pairing is related to the concentration of FAC in the extracellular medium, an assay for FAC was developed using standard test cells. The rate of release of FAC into the medium was measured in cells transferred from growth medium. It was found that a) FAC production is rapid, being detectable within 15 min after shift down; b) within 1 hr, sufficient FAC is released by the cells to support near maximal pairing activity among test cells; and c) cycloheximide completely blocks release of FAC. It was further demonstrated that addition of high‐titer FAC to freshly shifted down cells did not shorten the delay period before conjugation. Therefore, the starvation period is a time during which a) FAC is released into the medium, and b) cells develop receptivity to mating interactions, with the latter being rate‐limiting for conjugation. FAC is produced by sexually immature cells, by cells in growth medium, and by cells starving in high ionic strength buffer, but not by nonmating amicronucleate cells of T. pyriformis. Cell interactions during mating are modulated by FAC, but only among developmentally receptive cells.