What are the key aspects of interaction between RNA polymerase II C-terminal domain phosphorylated on tyrosine-1 and the elongation factors

Post-translational modifications of the consensus motif Y1-S2-P3-T4-S5-P6-S7 of the C-terminal domain (CTD) of RNA polymerase II are since last decade known as the “CTD code”. These modifications are dynamic and specific for each phase of the transcriptional cycle. Increased phosphorylation levels of Y1 during the productive elongation prevents binding of termination factors, and stimulates recruitment of elongation factors. However, there is no structural information on how the phosphotyrosine modified CTD is recognized by these elongation factors. To investigate phosphotyrosine recognition, we employed integrative approach to structural biology–namely combination of solution nuclear magnetic resonance, small angle X-ray scattering, mass spectrometry and X-ray crystallography, supported by functional studies with point/multiple mutations. We will present the structural data for phosphotyrosine recognition within the CTD by the elongation factor, which help to decipher how this important CTD modification mark is read out by transcription factors.