Abstract
DNA is constantly exposed to endogenous and exogenous damage. Various types of DNA repair counteract highly toxic DNA double-strand breaks (DSBs) to maintain genome stability. Recent findings suggest that the human DNA damage response (DDR) utilizes small RNA species, which are produced as long non-coding (nc)RNA precursors and promote recognition of DSBs. However, regulatory principles that control production of such transcripts remain largely elusive. Here we show that the Abelson tyrosine kinase c-Abl/ABL1 causes formation of RNA polymerase II (RNAPII) foci, predominantly phosphorylated at carboxy-terminal domain (CTD) residue Tyr1, at DSBs. CTD Tyr1-phosphorylated RNAPII (CTD Y1P) synthetizes strand-specific, damage-responsive transcripts (DARTs), which trigger formation of double-stranded (ds)RNA intermediates via DNA-RNA hybrid intermediates to promote recruitment of p53-binding protein 1 (53BP1) and Mediator of DNA damage checkpoint 1 (MDC1) to endogenous DSBs. Interference with transcription, c-Abl activity, DNA-RNA hybrid formation or dsRNA processing impairs CTD Y1P foci formation, attenuates DART synthesis and delays recruitment of DDR factors and DSB signalling. Collectively, our data provide novel insight in RNA-dependent DDR by coupling DSB-induced c-Abl activity on RNAPII to generate DARTs for consequent DSB recognition.