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.
