Transcription and processing of ß-tubulin messenger RNA in Leishmania donovani promastigotes.

Transcription of the multicopy ß-tubulin locus in Leishmania donovani promastigotes was examined by nucleic acid hybridization techniques. By northern analysis of promastigote RNA multiple ß-tubulin mRNAs were detected. The major species of 2·2 kb RNA is derived from the tandem repeat cluster of ß-tubulin genes, the other two (2·4 and 2·6 kb) are presumably derived from dispersed genomic loci. Combined S1-nuclease and primer extension mapping experiments demonstrated the presence of a single 5'-terminus with a 35 nucleotide spliced-leader sequence. The 3'-termini are heterogeneous. The development of a nuclear run-on system in Leishmania for studying transcription of individual genes is reported. Active but transient RNA polymerase II activity was observed in this system. Using specific DNA probes for labelled run-on RNA it was shown that ß-tubulin transcription occurs asymmetrically (i.e., on one strand of the DNA template) in an α-amanitin sensitive manner. The significance of these results for the life cycle of the parasite is discussed.