Alterations in gene expression induced by a specific cell interaction during mating in Tetrahymena thermophila

Abstract

Conjugation in Tetrahymena thermophila is preceded by a specific cell interaction, co-stimulation, which occurs between starved, competent mating types. Using [ 35S]methionine pulse-labelling, SDS-polyacrylamide gel electrophoresis and autoradiography, we observed a substantial increase in the relative synthetic rate of an 80 kD polypeptide (designated p80) in total-cellular protein. This change begins 15–30 min after mating types are mixed, but does not occur if starved mating types are not mixed. It does not take place when a competent mating type is mixed with a non-mating strain, nor is p80 induced in cells of one mating type by the cell-free starvation conditioned medium of a second mating type. Therefore, there is a specific association between co-stimulation and the induction of p80. Electrophoresis of macronuclei isolated following pulse-labelling showed that the change in p80 could also be observed in macronuclear non-histone protein. Induction of p80 was observed in cells incubated with 25 μg/ml actinomycin D (actD), but was completely inhibited by 250 μg/ml of this drug. It appears that p80 may be specifically induced at the transcriptional level by direct cell-cell interaction. We discuss the possibility that this protein may play a regulatory role in changing the genetic program expressed by macronuclei in preparation for cell pairing.