Mini-exon derived RNA gene of Leishmania donovani: structure, organization and expression

Abstract

Mini-exon derived RNA is a small nuclear RNA of trypanosomatid protozoa such as Leishmania which donates its 5'-terminal 39 nucleotides to the 5'-ends of cellular messenger RNAs by trans-splicing. We have cloned a mini-exon derived RNA gene from Leishmania donovani and studied its organization and expression. About 200 copies of the gene per haploid genome are organized as a tandem repeat on a single chromosome. The gene is transcribed as a 95-nucleotide RNA. The first 39 nucleotides of mini-exon derived RNA is also found at the 5'-terminus of a cellular mRNA (β-tubulin), thus confirming its identity. Sequence analysis of the gene and its flanking regions showed that while classical RNA polymerase II promoter elements such as TATA and CAAT are absent from the 5'-upstream region, intragenic sequence motifs resembling RNA polymerase III promoter elements are present. The implications of this finding for mini-exon derived RNA expression are discussed.