RNA ligands generated against complex nuclear targets indicate a role for U1 snRNP in co-ordinating transcription and RNA splicing.

RNA ligands were generated against various gene products present in HeLa nuclear extract. Functional profiling was performed to identify RNA ligands that modulate RNA polymerase II (pol II)-mediated transcription. Unexpectedly, four of the eight inhibitor ligands identified by this screen contained an 11-nucleotide sequence identical to the 5'-splice site of eukaryotic pre-mRNAs. Such ligands were shown to impede pre-initiation complex assembly on a cytomegalovirus promoter. In addition, U1 small nuclear ribonucleoprotein particles (snRNP) and pol II had been co-immunoprecipitated in the absence of transcription. These results suggest a role for U1 snRNP in co-ordinating transcription and RNA splicing.