Sub1/PC4, a multifaceted factor: from transcription to genome stability.

Yeast Sub1 and human PC4, two DNA-binding proteins, were originally identified as transcriptional coactivators with a role during transcription preinitiation/initiation. Indeed, Sub1 is a PIC component, and both PC4 and Sub1 also influence the initiation-elongation transition. Moreover, in the specific case of Sub1, it has been clearly reported that it influences processes downstream during mRNA biogenesis, such as transcription elongation, splicing and termination, and even RNAPII phosphorylation/dephosphorylation. Although Sub1 mechanism of action has been mostly unknown up to date, thanks to the recent finding that Sub1 directly interacts with the RNAPII stalk domain, we can envision how it can modulate so many processes. In addition, Sub1 and PC4 participate in RNAPIII transcription as well, and much additional evidence indicates an evolutionarily conserved role for Sub1 and PC4 in the maintenance of genome stability. In this regard, the most novel function of Sub1 and PC4 has been related to the ability of these proteins to bind G-quadruplex DNA structures that may arise as a consequence of the transcription process.