The heterogeneous nuclear ribonucleoprotein C protein tetramer binds U1, U2, and U6 snRNAs through its high affinity RNA binding domain (the bZIP-like motif).
Based on UV cross-linking experiments, it has been reported that the C protein tetramer of 40 S heterogeneous nuclear ribonucleoprotein complexes specifically interacts with stem-loop I of U2 small nuclear RNA (snRNA) (Temsamani, J., and Pederson, T. (1996) J. Biol. Chem. 271, 24922-24926), that C protein disrupts U4:U6 snRNA complexes (Forne, T., Rossi, F., Labourier, E., Antoine, E., Cathala, G., Brunel, C., and Tazi, J. (1995) J. Biol. Chem. 270, 16476-16481), that U6 snRNA may modulate C protein phosphorylation (Mayrand, S. H., Fung, P. A., and Pederson, T. (1996) Mol. Cell. Biol. 16, 1241-1246), and that hyperphosphorylated C protein lacks pre-mRNA binding activity. These findings suggest that snRNA-C protein interactions may function to recruit snRNA to, or displace C protein from, splice junctions. In this study, both equilibrium and non-equilibrium RNA binding assays reveal that purified native C protein binds U1, U2, and U6 snRNA with significant affinity ( approximately 7.5-50 nM) although nonspecifically. Competition binding assays reveal that U2 snRNA (the highest affinity snRNA substrate) is ineffective in C protein displacement from branch-point/splice junctions or as a competitor of C protein's self-cooperative RNA binding mode. Additionally, C protein binds snRNA through its high affinity bZLM and mutations in the RNA recognition motif at suggested RNA binding sites primarily affect protein oligomerization.
Department of Molecular Biology, Vanderbilt University, Nashville, Tennessee 37235, USA.
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Shahied-Milam
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Soltaninassab
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Iyer
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LeStourgeon
D006367:HeLa Cells; D034441:Heterogeneous-Nuclear Ribonucleoproteins; D006801:Humans; D010766:Phosphorylation; D011485:Protein Binding; D012342:RNA, Small Nuclear / Q000737:chemistry / Q000378:metabolism*; D016601:RNA-Binding Proteins / Q000378:metabolism*; D012261:Ribonucleoproteins / Q000737:chemistry / Q000378:metabolism*; D014529:Uridine / Q000378:metabolism
D034441:Heterogeneous-Nuclear Ribonucleoproteins; D012342:RNA, Small Nuclear; D016601:RNA-Binding Proteins; D012261:Ribonucleoproteins; D014529:Uridine