Final answer:
The addition of the poly A tail to a eukaryotic mRNA requires a 3'-OH group on the RNA, poly A polymerase, a conserved sequence (AAUAAA) near the 3' end of the RNA, and ATP.
Step-by-step explanation:
The addition of the poly A tail to a eukaryotic mRNA requires several components: a 3'-OH group on the RNA, poly A polymerase, and a conserved sequence (AAUAAA) near the 3' end of the RNA. Additionally, the addition of the poly A tail requires ATP as the source of adenine residues.