Figure 1. Ubiquitination at the RPA-coated ssDNA platform under replication stress.

ATR activation promotes PRP19 recruitment to RPA-coated ssDNA, PRP19 and RFWD3 catalyze RPA poly-ubiquitination at the stalled replication fork. ATR-ATRIP is recruited to stalled replication forks by directly binding to RPA. Recruitment of ATR-ATRIP is also promoted by RPA ubiquitination, and that might be mediated by an uncharacterized protein (protein X) as the lack of ubiquitin binding domain on ATR-ATRIP.