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Intron retention and recognition in the microsporidian encephalitozoon cuniculi Lee, Renny

Abstract

Microsporidia are unicellular fungi that are intracellular parasites of animals, including humans. They are both complex and simple, armed with a sophisticated infection apparatus and possessing the smallest eukaryotic nuclear genomes. The microsporidian Encephalitozoon cuniculi has a genome size of 2.9 Mb, which is smaller than many bacterial genomes. Genome reduction and compaction in size, content, and form has been interpreted as an adaptation to parasitism. One of the effects of genome size reduction concerns intron evolution — E. cuniculi has retained only a few extremely short spliceosomal introns. This thesis examines the splicing of introns in the spore stage. The introns were retained in spores, suggesting life-stage specific splicing and splicing inhibition. How the short introns are recognized was also examined. Unique splicing signal motifs were predicted, and were used to find additional introns. The intron density was doubled for this species, and I also obtained data that counter current views about intron evolution in compacted genomes with low intron densities. I also predict that E. cuniculi introns are recognized in a unique way by the spliceosome.

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