2 DIFFERENT MACRONUCLEAR EF-1-ALPHA-ENCODING GENES OF THE CILIATE EUPLOTES-CRASSUS ARE VERY DISSIMILAR IN THEIR SEQUENCES, COPY NUMBERS ANDTRANSCRIPTIONAL 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 p otential of differential gene expression during different phases of de velopment, or as gene dosage adaptation to the need of high-level prod uction of the gene products, Since ciliates can differentially amplify their genes, the latter argument would lead to the expectation of onl y one EFA gene in the macronucleus, However, we have found two such ge nes which strongly differ in both copy number and codon usage. Both tr anscripts are detectable at very different levels. The expression of t he genes takes place both in the vegetative and sexual phases, i.e., d uring conjugation.