Genomic 'Haircut' Makes World's Tiniest Genome Even Smaller
ScienceDaily (Sep. 21, 2010) — The world's tiniest nuclear genome appears to have "snipped off the ends" of its chromosomes and evolved into a lean, mean, genome machine that infects human cells, according to research published September 21 by University of British Columbia scientists.
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E. intestinalis (the little white dots) infecting human cells. (Credit: L. Weiss)
Until recently, E. cuniculi, a parasitic fungus commonly found in rabbits that can also be fatal to immunocompromised humans, has been widely regarded as having the smallest known nuclear genome. At 2.9 millions base pairs (Mbp) and approximately 2,000 genes, the genome of E. cuniculi is less than one-two thousandth the size of the human genome.
But now, a team of researchers led by UBC Botany Prof. Patrick Keeling sequenced the genome of a closely related parasite that makes the E. cuniculi genome seem positively king-sized. The genome of E. intestinalis, a sister species of E. cuniculi that infects human intestines, is 20 per cent smaller, at only 2.3Mbp.
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The complete sequence of the smallest known nuclear genome from the microsporidian Encephalitozoon intestinalis
Nicolas Corradi, Jean-François Pombert, Laurent Farinelli, Elizabeth S. Didier & Patrick J. Keeling
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Nature Communications 1 , Article number: 77
doi:10.1038/ncomms1082Received 01 June 2010 Accepted 25 August 2010 Published 21 September 2010
Abstract
The genome of the microsporidia Encephalitozoon cuniculi is widely recognized as a model for extreme reduction and compaction. At only 2.9 Mbp, the genome encodes approximately 2,000 densely packed genes and little else. However, the nuclear genome of its sister, Encephalitozoon intestinalis, is even more reduced; at 2.3 Mbp, it represents a 20% reduction from an already severely compacted genome, raising the question, what else can be lost? In this paper, we describe the complete sequence of the E. intestinalisgenome and its comparison with that of E. cuniculi. The two species share a conserved gene content, order and density over most of their genomes. The exceptions are the subtelomeric regions, where E. intestinalis chromosomes are missing large gene blocks of sequence found in E. cuniculi. In the remaining gene-dense chromosome 'cores', the diminutive intergenic sequences and introns are actually more highly conserved than the genes themselves, suggesting that they have reached the limits of reduction for a fully functional genome.
Subject terms: Biological sciences, Evolution, Genetics, Genomics, Microbiology, Parasitology
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