Sequence heterogeneity, multiplicity, and genomic organization of α- and β-tubulin genes in sea urchins

We analyzed the multiplicity, heterogeneity, and organization of the genes encoding the α and β tubulins in the sea urchin Lytechinus pictus by using cloned complementary deoxyribonucleic acid (cDNA) and genomic tubulin sequences. cDNA clones were constructed by using immature spermatogenic testis polyadenylic acid-containing ribonucleic acid as a template, α- and β-tubulin clones were identified by hybrid selection and in vitro translation of the corresponding messenger ribonucleic acids, followed by immunoprecipitation and two-dimensional gel electrophoresis of the translation products. The α cDNA clone contains a sequence that encodes the 48 C-terminal amino acids of α tubulin and 104 base pairs of the 3' nontranslated portion of the messenger ribonucleic acid. The β cDNA insertion contains the coding sequence for the 100 C-terminal amino acids of β tubulin and 83 base pairs of the 3' noncoding sequence. Hybrid selections performed at different criteria demonstrated the presence of several heterogeneous, closely related tubulin messenger ribonucleic acids, suggesting the existence of heterogeneous α- and β-tubulin genes. Hybridization analyses indicated that there are at least 9 to 13 sequences for each of the two tubulin gene families per haploid genome. Hybridization of the cDNA probes to both total genomic DNA and cloned germline DNA fragments gave no evidence for close physical linkage of α-tubulin genes with β-tubulin genes at the DNA level. In contrast, these experiments indicated that some genes within the same family are clustered.