Transcriptional mapping of Leishmania enrietti tubulin mRNAs

We have mapped the mRNAs for alpha- and beta-tubulins of Leishmania enriettii promastigotes and amastigotes and have demonstrated that each RNA contains a 35 nucleotide sequence on its 5' end which is not encoded contiguously with the rest of the message. Sequencing of the 5' end of the alpha- and beta-tubulin mRNAs revealed that this 35 nucleotide leader sequence is identical in both messages and that it is homologous to the spliced leader found on the 5' end of mRNAs in the related parasite Trypanosoma brucei. Additionally, we have sequenced regions of the alpha- and beta-tubulin genomic clones upstream from the mRNA encoding regions and have shown that the leader sequence is not encoded within these regions of DNA. Hence, Leishmania tubulin mRNAs may be synthesized by a discontinuous transcription process that links together the transcription products of two separate gene families, as suggested previously by others for the assembly of T. brucei mRNAs. Homologies between the Leishmania alpha- and beta-tubulin genes themselves and between these genes and the T. brucei alpha- and beta-tubulin genes have revealed sequences which may be important in synthesis or processing of Leishmania tubulin mRNAs.