Two different macronuclear EF-1 alpha-encoding genes of the ciliate Euplotes crassus are very dissimilar in their sequences, copy numbers and transcriptional activities.

Genes (EFA) encoding the translation elongation factor EF-1 alpha (EFA) or the prokaryotic homolog EFTu frequently occur in multiple copies in the same organism. This has been interpreted either in terms of a potential of differential gene expression during different phases of development, or as gene dosage adaptation to the need of high-level production of the gene products. Since ciliates can differentially amplify their genes, the latter argument would lead to the expectation of only one EFA gene in the macronucleus. However, we have found two such genes which strongly differ in both copy number and codon usage. Both transcripts are detectable at very different levels. The expression of the genes takes place both in the vegetative and sexual phases, i.e.,during conjugation.