Rpb4 and Rpb7: subunits of RNA polymerase II and beyond.

RNA Polymerase II (pol II) is a large multi-subunit complex that is responsible for the synthesis of all eukaryotic mRNAs. Its correct and timely recruitment to promoter regions is a crucial step of transcription regulation, involving complicated and well-controlled networks of protein-DNA and protein-protein interactions. The best-studied pol II is the yeast complex consisting of 12 subunits (Rpb1-12). Rpb4 and Rpb7 form a dissociable heterodimer (Rpb4/7). The unique location of Rpb4/7 within the transcription initiation complex, and its capacity to interact with various transcription factors, suggest that it provides important links to the network of interactions that control transcription initiation. Moreover, Rpb4/7 executes some non-transcriptional activities, including mRNA transport. Hence, Rpb4/7 functions at the interface of transcriptional and post-transcriptional machinery.