Final answer:
Phosphorylating the tail of RNA Polymerase II allows the enzyme to initiate transcription and start synthesizing mRNA.
Step-by-step explanation:
The purpose of phosphorylating the tail of RNA Polymerase II is to initiate transcription and allow the enzyme to start synthesizing mRNA.
Phosphorylation adds phosphates to the aminoterminus of RNA Polymerase II, which leads to the dissociation of some transcription factors from the initiation complex.
This phosphorylated RNA Polymerase II can then begin transcribing the DNA template into mRNA.