Contribution of the individual subunits of protein kinase CK2 and of hPrp3p to the splicing process

We have recently shown that protein kinase CK2 binds to the splice factor hPrp3p. Moreover, CK2 phosphorylates hPrp3p in vitro and in vivo. Here we analysed the spliceosome for the presence of individual subunits of CK2. By cell fractionation experiments we found that CK2 alpha, CK2 alpha', the spliceosome specific SmB/B' and hPrp3p protein co-localize in the nucleus. A sucrose density gradient analysis revealed that the individual subunits of CK2 co-sedimented at least in part with the SmB/B' protein. We further show by co-immune precipitation experiments that CK2 alpha is associated with the U4/U6*U5 tri-snRNP specific protein 61K. In vitro splice assays with nuclear extracts depleted from CK2 alpha, CK2 alpha' and hPrp3p, respectively, revealed that CK2 alpha and hPrp3p are absolutely necessary for an efficient splicing whereas CK2 alpha' seems to be dispensable. Furthermore, these data support the notion about individual roles for CK2 alpha and CK2 alpha' in the splicing process.