Total RNA was isolated after cell lysis (Qiagen Tissue Ruptor) using the Qiagen RNeasy Maxi Kit. The entire total RNA samples were subjected to mRNA isolation by Dynabeads Oligo-dT25 beads (Invitrogen). UMI-STARR-Seq libraries were UMI-tagged and prepared for NGS as previously described (Arnold et al., 2013, Neumayr et al., 2019).