Human-mouse comparative analysis reveals that branch-site plasticity contributes to splicing regulation

Guy Kol, Galit Lev-Maor, Gil Ast*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

80 Scopus citations


The formation of base-pairing between the branch-site (BS) sequence and the U2 snRNP is an important step in mRNA splicing. We developed a new algorithm to identify both the BS sequence and the polypyrimidine tract (PPT) and validated its predictions experimentally. To assess BS conservation between human and mouse, we assembled and analyzed 46 812 and 242 constitutively and alternatively spliced orthologs of human-mouse intron pairs, respectively. Combinations of BSs and PPTs can be found in most of the constitutive and alternative introns. The average distance between the BS and the 3′ splice site (3′ss) is 33-34 nt. Acceptor-like AG dinucleotides that resided between the predicted BS and the 3′ss were found to appear mostly within 5 nt, but not more than 19 nt, downstream of the BS. However, although 32% of homologous alternatively spliced BS sequences were fully conserved between human and mouse, only a small fraction (3%) of homologous constitutive counterparts was fully conserved. This indicates that the full sequence of the BS is under weak purifying selection in constitutively spliced introns and further strengthens the view that the BS sequence is just one of several factors determining the ability of the splicing machinery to identify the BS location. Mutations in the putative BS revealed a shift from constitutive to alternative splicing, and it also controls the inclusion/skipping ratio in alternative splicing. This suggests a role for BS sequences in regulated splicing.

Original languageEnglish
Pages (from-to)1559-1568
Number of pages10
JournalHuman Molecular Genetics
Issue number11
StatePublished - 1 Jun 2005


FundersFunder number
Chief Scientist of the Israel Health Ministry
FD Hope
German Israeli Project Cooperation Program
Israel Science Foundation717/01, 1449/ 04


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