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Background  Alpha tubulin is a fundamental component of the cytoskeleton which is responsible for cell shape and is involved in cell division, ciliary and flagellar motility and intracellular transport. Alpha tubulin gene expression varies according to the morphological changes suffered by  Leishmania  in its life cycle. However, the objective of studying the mechanisms responsible for the differential expression has resulted to be a difficult task due to the complex genome organization of tubulin genes and to the non-conventional mechanisms of gene regulation operating in  Leishmania .    Results  We started this work by analyzing the genomic organization of  α-tubulin  genes in the  Leishmania braziliensis  genome database. The genomic organization of  L. braziliensis α-tubulin  genes differs from that existing in the  L. major  and  L. infantum  genomes. Two loci containing  α-tubulin  genes were found in the chromosomes 13 and 29, even though the existence of sequence gaps does not allow knowing the exact number of genes at each locus. Southern blot assays showed that  α-tubulin  locus at chromosome 13 contains at least 8 gene copies, which are tandemly organized with a 2.08-kb repetition unit; the locus at chromosome 29 seems to contain a sole  α-tubulin  gene. In addition, it was found that  L. braziliensis α-tubulin  locus at chromosome 13 contains two types of  α-tubulin  genes differing in their 3′ UTR, each one presumably containing different regulatory motifs. It was also determined that the mRNA expression levels of these genes are controlled by post-transcriptional mechanisms tightly linked to the growth temperature. Moreover, the decrease in the  α-tubulin  mRNA abundance observed when promastigotes were cultured at 35°C was accompanied by parasite morphology alterations, similar to that occurring during the promastigote to amastigote differentiation.    Conclusions  Information found in the genome databases indicates that  α-tubulin  genes have been reorganized in a drastic manner along  Leishmania  speciation. In the  L. braziliensis  genome database, two loci containing  α-tubulin  sequences were found, but only the locus at chromosome 13 contains the prototypic  α-tubulin  genes, which are repeated in a head-to-tail manner. Also, we determined that the levels of  α-tubulin  mRNAs are down-regulated drastically in response to heat shock by a post-transcriptional mechanism which is dependent upon active protein synthesis.

Alpha tubulin genes from Leishmania braziliensis:genomic organization, gene structure and insights on their expression