The human cap-binding complex is functionally connected to the nuclear RNA exosome

Nuclear processing and quality control of eukaryotic RNA is mediated by the RNA exosome which is regulated by accessory factors. However the mechanism of exosome recruitment to its ribonucleoprotein (RNP) targets remains poorly understood. Here we report a physical link between the human exosome and the cap-binding complex (CBC). The CBC associates with the ARS2 protein to form CBC-ARS2 (CBCA) and then further connects together with the ZC3H18 protein to the nuclear exosome targeting (NEXT) complex thus forming CBC-NEXT (CBCN). RNA immunoprecipitation using CBCN factors as well as the analysis of combinatorial depletion of CBCN and exosome components underscore the functional relevance of CBC-exosome bridging at the level of target RNA. Specifically CBCA suppresses read-through products of several RNA families by promoting their transcriptional termination. We suggest that the RNP 5' cap links transcription termination to exosomal RNA degradation through CBCN.