Distribution of conventional and nonconventional introns in tubulin (α and β) genes of euglenids

The nuclear genomes of euglenids contain three types of introns: conventional spliceosomal introns, nonconventional introns for which a splicing mechanism is unknown (variable noncanonical borders, RNA secondary structure bringing together intron ends), and so-called intermediate introns, which comb...

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Bibliographic Details
Published in:Molecular biology and evolution 2014-03, Vol.31 (3), p.584-593
Main Authors: Milanowski, Rafał, Karnkowska, Anna, Ishikawa, Takao, Zakryś, Bozena
Format: Article
Language:English
Subjects:
Base Sequence
Discoveries
Euglenida - genetics
Evolution, Molecular
Genes, Protozoan - genetics
Genomes
Genomics
Hypotheses
Introns - genetics
Models, Genetic
Molecular biology
Molecular Sequence Data
Nucleic Acid Conformation
Phylogeny
Proteins
Ribonucleic acid
RNA
Tubulin - genetics
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Summary:The nuclear genomes of euglenids contain three types of introns: conventional spliceosomal introns, nonconventional introns for which a splicing mechanism is unknown (variable noncanonical borders, RNA secondary structure bringing together intron ends), and so-called intermediate introns, which combine features of conventional and nonconventional introns. Analysis of two genes, tubA and tubB, from 20 species of euglenids reveals contrasting distribution patterns of conventional and nonconventional introns--positions of conventional introns are conserved, whereas those of the nonconventional ones are unique to individual species or small groups of closely related taxa. Moreover, in the group of phototrophic euglenids, 11 events of conventional intron loss versus 15 events of nonconventional intron gain were identified. A comparison of all nonconventional intron sequences highlighted the most conserved elements in their sequence and secondary structure. Our results led us to put forward two hypotheses. 1) The first one posits that mutational changes in intron sequence could lead to a change in their excision mechanism--intermediate introns would then be a transitional form between the conventional and nonconventional introns. 2) The second hypothesis concerns the origin of nonconventional introns--because of the presence of inverted repeats near their ends, insertion of MITE-like transposon elements is proposed as a possible source of new introns.
ISSN:0737-4038
1537-1719
DOI:10.1093/molbev/mst227