Cloning and sequencing of tubulin cDNAs from Artemia franciscana: evidence for differential expression of α- and β-tubulin genes

Tubulin is a heterodimeric protein composed of alpha- and beta-tubulin. In most organisms, they are encoded by multiple gene families whose members are subject to differential regulation. The objective of the work described herein was to better understand tubulin gene expression in the extremophile Artemia franciscana To this end tubulin cDNAs were cloned and sequenced. alphaAT2, an alpha-tubulin cDNA, differed by one nucleotide from alphaAT1, a previously cloned Artemia cDNA. This change, possibly generated by allelic variation, caused an M313V substitution in alpha-tubulin. The amino acid sequence of beta-tubulin encoded by betaAT1, one of only a very limited number of cloned crustacean beta-tubulin cDNA sequences yet available, and the first from Artemia, was similar to other beta-tubulins. However, betaAT1 possessed four degenerate TATA boxes in the 5' untranslated region, although authentic TATA and CCAAT boxes occurred in the 3' non-coding sequence. Analyses by quantitative PCR demonstrated that the amount of tubulin mRNA declined relative to total mRNA in progressive life history stages of Artemia and also that the organism contained more alphaAT2- than betaAT1-tubulin mRNA at all developmental phases examined.