POLR2A and chromosome-type aberration frequency: When elongating RNA Pol II stalls on obstacles, it becomes ubiquitylated at lysine 1268 (K1268) on its catalytic subunit, RPB1,5,39 and this modification is essential for cells to survive DNA damage.5 RPB1 K1268 on elongation-stalled RNA Pol II is targeted by at least two different E3 ubiquitin ligases, Cockayne Syndrome A (CSA) and a yet unknown ligase, leading to either stabilization of the transcription-coupled nucleotide excision repair complex39,40 or to RPB1 degradation as the last-resort pathway,5,41,42 respectively.