Analysis of Euglena gracilis alpha-, beta- and gamma-tubulin genes: introns and pre-mRNA maturation

We have cloned and analyzed alpha-, beta- and gamma-tubulin genes from Eugl ena gracilis. The gamma-tubulin genes are 6-10 times longer than the alpha- and beta-tubulin genes, owing to the presence of numerous introns. These i ntrons an all of the conventional type, whereas the alpha- and hera-tubulin genes contain both conventional and non-conventional introns. This is the first time that both types of introns have been found in the same gene. In the E. gracilis genome there are two genes for each tubulin, but the level of gamma-tubulin mRNA is 60 times lower than that of alpha- and beta-tubuli n RNAs. The distinctive structure of gamma-tubulin genes prompted us to inv estigate the maturation of its pre-mRNA. We show that trans-splicing occurs before the cis-splicing of the first intron of the pre-mRNA and that polya denylation occurs after the cis-splicing of the last intron of the pre-mRNA . We propose that mRNA processing is likely to play a role in regulating th e amounts of different tubulins in E. gracilis.