Abstract
Exons with predicted branch points were identified from a large dataset of human exons and the importance of these branch points for splicing was verified.
Highlights
The three consensus elements at the 3' end of human introns - the branch point sequence, the polypyrimidine tract, and the 3' splice site AG dinucleotide - are usually closely spaced within the final 40 nucleotides of the intron
When plotted as log(number of exons) versus log(size of EZ), the distribution of AG dinucleotide exclusion zones (AGEZ) values did not obviously exhibit a simple excess of high values compared with the curves for the other dinucleotides
Because scanning for the 3' splice site takes place downstream from distant branch points (dBPs), we expect a selective pressure against AG dinucleotides between dBPs and the 3' splice site, and a general lack of selective pressure against AGs upstream of BPs
Summary
The three consensus elements at the 3' end of human introns - the branch point sequence, the polypyrimidine tract, and the 3' splice site AG dinucleotide - are usually closely spaced within the final 40 nucleotides of the intron. At the 3' end of the intron, usually within about 40 nucleotides upstream of the exon, there are three elements (in 5' to 3' order): a branch point sequence (BPS); a polypyrimidine tract (PPT); and the 3' splice site itself, which consists of the invariant AG dinucleotide at the end of the intron, usually preceded by a pyrimidine residue. Recognition of these consensus elements by various trans-acting protein and RNA splicing factors leads to assembly of the spliceosome, within which the two chemical steps of splicing occur [8]. The 3'-OH of the 5' exon attacks the 3' splice site, leading to production of the spliced RNA and the excised intron, still in the lariat configuration
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