Introns of Entamoeba histolytica and Entamoeba dispar

The genome of Entamoeba histolytica is considered to possess very few intervening sequences (introns), as only 5 intron-containing genes from this protozoan parasite have been reported so far. However, while sequencing a number of genomic contigs as well as three independent genes coding for ribosomal protein L27a, we have identified 9 additional intron-containing genes of E. histolytica and the closely related species Entamoeba dispar,indicating that introns are more common in these organisms than previously suggested. The various amoeba introns are relatively short comprising between 46 and 115 nucleotides only and have a higher AT-content compared to thecorresponding exon sequences. In contrast to higher eukaryotes, amoeba introns do not contain a well-conserved branch point consensus, and have extended donor and acceptor splice sites of the sequences GTTTGTT and TAG, respectively. Consistent with the close phylogenetic relationship of E. histolytica and E. dispar, the position and length of introns is conserved between the two species but the degree of sequence identity is reduced compared to orthologous coding regions.