Nuclear factors binding to the mini-exon repeat of Trypanosoma brucei

In trypanosomes and related kinetoplastida a common short 5' leader sequence is encoded by the highly repetitive mini-exon gene and added to all protein coding mRNAs by trans-splicing. To initiate a search for transcription factors associated with transcription of the mini-exon we have used an electrophoretic mobility shift assay to detect trypanosome nuclear factors which interact specifically with mini-exon DNA. A factor present in the nuclei of both infectious bloodstream forms and non-infectious culture forms of Trypanosoma brucei was shown by DNAase I footprinting and oligonucleotide competition to bind 5' to the transcription start site of the mini-exon. A second factor which bound to the mini-exon itself at a sequence conserved in other kinetoplastida was evident only in the nuclei of infectious bloodstream forms.