title: The monogenetic kinetoplastid protozoan, Crithidia fasciculata, contains a transcriptionally active, multicopy mini-exon sequence.
abstract: A repeated sequence from the Crithidia fasciculata nuclear genome has been isolated which is homologous to the mini-exon genes of other kinetoplastid protozoa. Sequence analysis of the 417 bp monomeric unit confirmed the presence of a 35 nt sequence within the repeat that is 77% homologous with the Trypanosoma brucei 35-mer mini-exon or spliced leader sequence. The repeat is present at approximately 250 copies per cell and is organized into one, or a few, large head to tail tandem clusters predominantly on a single chromosome. The mini-exon repeat unit hybridizes to a major 84 nt and a minor 87 nt poly (A)- steady state transcript, the first 35 nts of which comprise the mini-exon sequence found at the 5' end of mRNAs in several other kinetoplastid species. The 3'-termini of the transcripts map to positions on the DNA sense strand directly preceeding a stretch of 8 thymidine residues. Crithidia represents the most primitive kinetoplastid species which apparently possesses a discontinuous type of mRNA processing, implying that this represents a conserved feature in possibly all genera of kinetoplastid protozoa.
mesh_terms: D000818:Animals; D001483:Base Sequence; D003421:Crithidia / Q000235:genetics*; D056890:Eukaryota / Q000235:genetics; D005091:Exons; D005796:Genes; D009693:Nucleic Acid Hybridization; D012689:Sequence Homology, Nucleic Acid; D014158:Transcription, Genetic; D014346:Trypanosoma brucei brucei / Q000235:genetics