DNA sequence and pattern of expression of the sea urchin (Paracentrotus lividus) α‐tubulin genes

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Abstract
To study the molecular aspects of the regulation of transcription of a multigene family, we have isolated and sequenced cDNA and genomic clones coding for the α‐tubulin of the sea urchin Paracentrotus lividus. Two cDNA clones, Pα 10 and Pα 4, contain respectively the coding information for 391 C‐terminal and for 338 N‐terminal amino acids of the 452 residues that constitute the complete protein. They show silent nucleotide substitutions only, suggesting that Pα 10 and Pα 4 represent the cloned copies of two allelic gene transcripts, which encode for two α‐tubulin isoforms with identical amino acid sequence in the region of the overlap. The comparison of the predicted amino acid sequence of the composite Pα 4–10 and of the mouse M α‐6 (Villasante et al., Mol. Cell Biol 1986; 6:2409–2419) reveals a conservation of 97% between the two polypeptides. By RNA blotting hybridization six major α‐tubulin transcripts were identified. Two, of 3.5 kb and 2.0 kb, are expressed in the unfertilized eggs and during early cleavage. The other two maternal mRNAs, of 2.4 kb and 1.8 kb, are expressed in both early and late cleavage embryos, but in the intestine the 1.8 kb RNA, which specifically reacted with the 3′ specific probe of the Pα 10 cDNA, is the only transcript detected. Finally, the 1.5 kb and 1.9 kb mRNAs represent the transcription of stage‐ and tissue‐specific genes, respectively. In fact, the former becomes detectable at blastula stage and accumulates during late development, whereas the latter is found in the testis only. The sequence data of the 3′ terminus of the α‐3 genomic clone suggests that it encodes for a divergent α‐tubulin, and it most probably corresponds to the testis‐specific gene.