Many trypanosome messenger RNAs share a common 5' terminal sequence

Area of Science:

• Molecular Biology
• Parasitology
• Genetics

Background:

• Trypanosoma brucei variant surface antigens initiate translation with a conserved 35-nucleotide sequence.
• This conserved sequence originates from a distinct mini-exon within a repetitive DNA element.
• Previous studies indicated trypanosomes possess numerous transcripts hybridizing to mini-exon probes, beyond those encoding surface antigens.

Purpose of the Study:

• To investigate the nature and prevalence of mini-exon sequences in Trypanosoma brucei transcripts.
• To determine if non-surface antigen mRNAs also utilize the mini-exon sequence.
• To elucidate the potential mechanism of mini-exon sequence incorporation into diverse mRNAs.

Main Methods:

• Hybridization of trypanosome transcripts with mini-exon probes.
• Cloning of complementary DNA (cDNA) from trypanosome mRNAs.
• Sequencing and analysis of selected cDNA clones containing mini-exon sequences.

Main Results:

• Transcripts containing the mini-exon sequence at their 5' end were identified.
• These transcripts were polyadenylated and lacked other sequences from the mini-exon repeat element.
• Analysis of 17 mini-exon containing cDNA clones revealed 13 derived from genes unrelated to surface antigens.

Conclusions:

• The mini-exon sequence serves as a common 5' element for a broad range of Trypanosoma brucei mRNAs.
• The widespread distribution suggests the mini-exon is a fundamental feature of trypanosome gene expression.
• Discontinuous transcription is proposed as a likely mechanism for linking the clustered mini-exon genes to the body of diverse mRNAs.