Beta tubulin gene of the parasitic protozoan Leishmania mexicana

A genomic DNA library was generated with Sau3A cut DNA derived from promastigotes of Leishmania mexicana amazonensis and the lambda vector EMBL3. The library was screened for β tubulin clones using ³²P-labeled heterologous probe of chicken β tubulin cDNA. From the various genomic clones the one designated 23.1, which gave the simplest hybridization banding pattern, was further characterized. The leishmanial insert DNA was subcloned into plasmid vectors and the resulting clones were designated as T11, T28 and T50. Using these clones leishmanial β tubulin coding region was sequenced by the dideoxy method. The result shows that the β tubulin has 445 amino acids, a carboxyl terminal tyrosine, and no intron. Leishmanial β tubulin has 93% amino acid sequence similarity with that of trypanosome and 82% with that of man; and there is a strong bias in codon usage for codons possessing guanine or cytosine in the third base.