UC San Diego

The nuclear Cap Binding Complex (CBC), which consists of a large subunit CBP80 and a small subunit CBP20, is structurally conserved from yeast to mammals. The complex has been implicated in multiple steps in mRNA processing including mRNA stability, pre-mRNA splicing, and mRNA export. The research described here provides evidence that the CBC plays a novel role in transcription through interactions with the RNA polymerase II (RNAPII), particularly through the C-terminal domain of the largest subunit (CTD). These interactions appear at least partially RNA independent and occur during active transcription. Although the CBC does not possess kinase or phosphatase activity, it does appear to affect CTD phosphorylation. One effect of this CBC-CTD interaction is regulation of the Nrd1 termination complex activity in attenuation of the IMP dehydrogenase gene IMD2 and its constituent cryptic unstable transcripts (CUTs). The involvement of the CBC with the RNA from capping to export and with RNAPII places it in an ideal position to provide regulatory feedback from the nascent RNA and RNA processing factors to the transcriptional machinery