Polypyrimidine tract binding protein inhibits IgM pre-mRNA splicing by diverting U2 snRNA base-pairing away from the branch point

Zheng, X.; Cho, S.; Moon, H.; Loh, T.J.; Oh, H.K.; Green, M.R.; Shen, H.

Rna 20(4): 440-446


ISSN/ISBN: 1469-9001
PMID: 24572809
DOI: 10.1261/rna.043737.113
Accession: 055049857

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The mouse immunoglobulin (IgM) pre-mRNA contains a splicing inhibitor that bears multiple binding sites for the splicing repressor polypyrimidine tract binding protein (PTB). Here we show that the inhibitor directs assembly of an ATP-dependent complex that contains PTB and U1 and U2 small nuclear RNAs (snRNAs). Unexpectedly, although U2 snRNA is present in the inhibitor complex, it is not base-paired to the branch point. We present evidence that inhibitor-bound PTB contacts U2 snRNA to promote base-pairing to an adjacent branch point-like sequence within the inhibitor, thereby preventing the U2 snRNA-branch point interaction and resulting in splicing repression. Our studies reveal a novel mechanism by which PTB represses splicing.