Coordination of transcription and pre-mRNA processing. mRNA-processing proteins associate with the C-terminal domain of Pol II. As the mRNA is synthesized, the capping enzyme (guanylyltransferase), splicing factors, and polyadenylation factors transfer from the Pol II CTD to the mRNA and process the mRNA as it is transcribed. (CBC is the cap-binding complex.) The mature transcript is used for multiple rounds of protein synthesis, then degraded.