STK19 drives transcription-coupled repair by stimulating repair complex stability, RNA Pol II ubiquitylation, and TFIIH recruitment.

Transcription-coupled nucleotide excision repair (TC-NER) efficiently eliminates DNA damage that impedes gene transcription by RNA polymerase II (RNA Pol II). TC-NER is initiated by the recognition of lesion-stalled RNA Pol II by CSB, which recruits the CRL4^CSA ubiquitin ligase and UVSSA. RNA Pol II ubiquitylation at RPB1-K1268 by CRL4^CSA serves as a critical TC-NER checkpoint, governing RNA Pol II stability and initiating DNA damage excision by TFIIH recruitment. However, the precise regulatory mechanisms of CRL4^CSA activity and TFIIH recruitment remain elusive. Here, we reveal human serine/threonine-protein kinase 19 (STK19) as a TC-NER factor, which is essential for correct DNA damage removal and subsequent transcription restart. Cryogenic electron microscopy (cryo-EM) studies demonstrate that STK19 is an integral part of the RNA Pol II-TC-NER complex, bridging CSA, UVSSA, RNA Pol II, and downstream DNA. STK19 stimulates TC-NER complex stability and CRL4^CSA activity, resulting in efficient RNA Pol II ubiquitylation and correct UVSSA and TFIIH binding. These findings underscore the crucial role of STK19 as a core TC-NER component.