Discontinuous synthesis of mRNA in trypanosomes.

Abstract

Many trypanosome mRNAs have the same sequence of 35 nucleotides at their 5′ end, encoded by a mini‐exon located in 1.35‐kb tandemly linked repeats. We have analysed nascent and steady‐state mini‐exon transcripts to determine how the mini‐exon sequence is joined to the main part of trypanosome mRNAs. We show here that steady‐state RNA from Trypanosoma brucei contains a transcript of 141 nucleotides that starts at the 5′ border of the mini‐exon. Isolated nuclei transcribe the segment corresponding to the 141 nucleotide RNA at a high rate; transcription of other areas of the 1.35‐kb mini‐exon repeat is approximately 750‐fold lower. We propose that transcription of protein‐coding genes in trypanosomes is discontinuous and involves the 141‐nucleotide transcript as an intermediate.