PMC:3475488 / 10209-11564 JSONTXT

{"project":"2_test","denotations":[{"id":"23105930-18478122-44845670","span":{"begin":643,"end":645},"obj":"18478122"},{"id":"23105930-16868079-44845671","span":{"begin":993,"end":995},"obj":"16868079"},{"id":"23105930-17617639-44845672","span":{"begin":1187,"end":1189},"obj":"17617639"}],"text":"Two-species 3n intron skew analysis\nFor all of the 10 genomes (Table 6), there were very similar numbers of 3n + 1 and 3n + 2 introns, and the percentages of 3n + 1 and 3n + 2 introns were within 0.8%. In contrast, the number of 3n introns varied much more widely, from 29.1% to 47.7%. In this study, two species' genome introns showed strongly skewed percentages, in that the 3n intron percentage was much lower or higher than the expected value (one-third). Such a skew suggests systematic errors in the intron prediction.\nThe green alga Ostreococcus lucimarinus has one of the highest gene densities known in eukaryotes, with many introns [28]. There was a striking excess of predicted 3n introns (47.7% of all predicted introns, 1,130) compared to 3n + 1 (25.8%, 611) and 3n + 2 (26.5%, 628) introns. In this case, many predicted 3n introns were not true introns but instead exons.\nThe unicellular green alga Ostreococcus tauri is the world's smallest free-living eukaryote known to date [29]. These predicted introns showed a deficit of 3n introns (29.1%, 1,262), much lower than 3n + 1 (35.8%, 1,553) and 3n + 2 (35%, 1,519) introns. This result is very close to previous studies [18]. In this case, 3n introns may be mistakenly regarded as coding sequences, whereas a 3n + 1 or 3n + 2 intron may be inferred from the disruption of the coding frame."}