Figure 1. Differential recruitment of RPAP2 to snRNA and protein-coding genes. On snRNA genes, RPAP2 is recruited through the pol II CTD phosphorylated on Ser7. RPAP2 association to snRNA promoters facilitates the recruitment of the 3′end processing Integrator subcomplex. During transcription, RPAP2 dephosphorylates Ser5 of the CTD, a step that might be required for efficient transcription and subsequent recruitment of the ‘catalytic core’ of the Integrator complex. On protein-coding genes, RPAP2 recruitment is independent of Ser7P and likely requires additional protein-protein interactions. Recruitment through Mediator/TFIID complex (1) and RPRD proteins (2) is proposed. Which CTD mark is required for binding the RPRD proteins is currently unknown. Similarly to snRNA genes, Ser5 dephosphorylation by RPAP2 might facilitate transcription and association of processing/termination factors.