The Tubα3 gene from Zea mays: structure and expression in dividing plant tissues

Abstract

A gene ( Tubα3) coding for an α-Tub, expressed in dividing tissues, has been cloned from Zea mays. The deduced amino acid (aa) sequence, 450 aa long, is very similar to the other plant α-Tub (85–89% homology) so far reported, and in particular to the other two aa sequences (α1-Tub and α2-Tub) already published from the same species (93% homology). The genomic structure is also very similar, having three introns located at the same positions as in the Tubα1 and Tubα2 genes, one of them placed at the same position in the homologous genes from Arabidopsis thaliana. Nevertheless, the noncoding sequences are very different from the two other maize genomic sequences. In particular, no homology has been found either in the 5′ upstream or in the 3′-untranslated sequences. Using specific 3′ probes, it has been possible to detect the mRNA coded by this gene in many of the plant organs measured, but its highest abundance is observed in the organs rich in dividing cells, a pattern correlated with that of the histone H4-encoding gene. A cDNA clone has been identified in maize coleoptiles and sequenced, confirming the expression of the Tubα3 in this organ. No prefential accumulation in any organ of the plant was found, in contrast with what was observed in the Tubα1 and Tubα2 genes already described. The Tubα gene family seems to consist in maize by at least two groups of homologous sequences, each one including a maximum of two or three coding units.