Roles of the phosphorylated SF3B1 in the activated spliceosome - experiment 1

SF3B1 is essential for assembly of B-complex spliceosome and activation of the Bact complex and undergoes dynamic phosphorylation and dephosphorylation during the splicing cycle. We have recently showed that the N-terminus of SF3B1 is phosphorylated during spliceosome activation by a little studied cyclin-dependent kinase 11 (CDK11) and remains hyperphosphorylated in catalytically active spliceosomes. However, little is known about the function of this N-terminal phosphorylation, about factors that “read” it, or about a spliceosome intermediate generated by CDK11 targeting. Here we demonstrate that CDK11 inhibition blocks spliceosome in a new intermediate during B to Bact transition. We now show that, phosphorylated SF3B1 N-terminus is crucial for binding of proteins during spliceosome activation.