Architecture and Distribution of Introns in Core Genes of Four Species.

Removal of introns from transcribed RNA represents a crucial step during the production of mRNA in eukaryotes. Available whole-genome sequences and expressed sequence tags (ESTs) have increased our knowledge of this process and revealed various commonalities among eukaryotes. However, certain aspects of intron structure and diversity are taxon-specific, which can complicate the accuracy of gene prediction methods. Using core genes, we evaluated the distribution and architecture of spliceosomal introns, and linked these characteristics to the accuracy of the predicted gene models of the genome of this fungus. We also evaluated intron distribution and architecture in , , and , and made comparisons with Results indicated that and the three other species have canonical 5' and 3' splice sites, but with subtle differences that are apparently not shared with those of other fungal genera. The polypyrimidine tract of introns was also found to be highly divergent among species and genes. Furthermore, the conserved adenosine nucleoside required during the first step of splicing is contained within unique branch site motifs in certain introns. Data generated here show that introns of , as well as , , and , are characterized by a number of unique features such as the CTHAH and ACCAT motifs of the branch site. Incorporation of such information into genome annotation software will undoubtedly improve the accuracy of gene prediction methods used for species and related fungi.