E3 ubiquitin-protein ligase RBX1
Cul4-RING E3 ubiquitin ligase complex
Structural basis of human transcription-DNA repair coupling.
Transcription-coupled DNA repair removes bulky DNA lesions from the genome<sup>1,2</sup> and protects cells against ultraviolet (UV) irradiation<sup>3</sup>. Transcription-coupled DNA repair begins when RNA polymerase II (Pol II) stalls at a DNA lesion and recruits the Cockayne syndrome protein CSB, the E3 ubiquitin ligase, CRL4<sup>CSA</sup> and UV-stimulated scaffold protein A (UVSSA)<sup>3</sup>. Here we provide five high-resolution structures of Pol II transcription complexes containing human transcription-coupled DNA repair factors and the elongation factors PAF1 complex (PAF) and SPT6. Together with biochemical and published<sup>3,4</sup> data, the structures provide a model for transcription-repair coupling. Stalling of Pol II at a DNA lesion triggers replacement of the elongation factor DSIF by CSB, which binds to PAF and moves upstream DNA to SPT6. The resulting elongation complex, EC<sup>TCR</sup>, uses the CSA-stimulated translocase activity of CSB to pull on upstream DNA and push Pol II forward. If the lesion cannot be bypassed, CRL4<sup>CSA</sup> spans over the Pol II clamp and ubiquitylates the RPB1 residue K1268, enabling recruitment of TFIIH to UVSSA and DNA repair. Conformational changes in CRL4<sup>CSA</sup> lead to ubiquitylation of CSB and to release of transcription-coupled DNA repair factors before transcription may continue over repaired DNA.