Structure and expression of Euplotes pheromone genes.

In some species of Euplotes (i. e., E. crassus, E. nobilii, E. octocarinatus and E. raikovi), substantial information has been obtained on the structure of the cell type-specific, water-borne signaling proteins (pheromones) that regulate the cell switching between the mating and growth stages of the life cycle. However, little is known about the organization and expression of the genes that encode pheromones at level of the transcriptionally active macronuclear genome. Based on the determination of the pheromone amino acid sequences, we used PCR approaches to clone a significant number of full-length (from telomere to telomere) pheromone genes in E. raikovi and E. nobilii. The comparative analysis of these genes showed that they form species-specific gene families in which each member is structurally closely related to all the other members by high levels of sequence identity. Marked variations were observed only at level of the sequences coding for the secreted pheromones. The intra-family sequence conservation of the 5’ and 3’ sub-telomeric (non-coding) regions (the 5’ regions are apparently conserved at a higher level than the 3’ regions) thus suggested a functional association between these regions and the mechanism of pheromone-gene expression. The study of this mechanism has consistently revealed not only that each gene synthesizes multiple mRNA’s starting from different sites of initiation of the transcription, but also that this synthesis requires the removal of introns from the 5’ non-coding gene regions.