The snRNP-free U1A complex Identification of the largest subunit as PSF, the polypyrimidine-tract binding protein-associated splicing factor

Lutz, C.S.; Cooke, C.; O'connor, J.P.; Kobayashi, R.; Alwine, J.C.

RNA (New York) 4(12): 1493-1499


ISSN/ISBN: 1355-8382
Accession: 033944166

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We have previously shown that a specific monoclonal antibody prepared against the U1A protein, MAb 12E12, is unique in its ability to recognize a form of U1A which is not associated with the U1snRNP. This unique form of U1A, termed snRNP-free U1A or SF-A, was found to be complexed with a novel set of non-snRNP proteins (O'Connor et al., 1997, RNA 3:1444-1455). Here we demonstrate that the largest protein in these SF-A complex(es), p105, is the polypyrimidine-tract binding protein-associated factor (PSF), an auxiliary splicing factor. We show that PSF copurifies and co-immunoprecipitates with SF-A from 293T cell nucleoplasm and that it interacts with SF-A in vitro. In addition, we show that MAb 12E12 inhibits both splicing and polyadenylation in an in vitro coupled splicing and polyadenylation reaction. This suggests that SF-A and/or the SF-A complex(es) perform an important function in both processing reactions and possibly in last axon definition.