Final answer:
False, the AAUAAA sequence near the 3' end of a eukaryotic mRNA is crucial for poly-adenylation but not for terminating the transcript. The cleavage which involves this sequence is separate from transcription termination and leads to the addition of the poly-A tail by poly-A polymerase.
Step-by-step explanation:
The AAUAAA sequence found near the 3' end of a eukaryotic mRNA is required not for terminating the transcript, but it is indeed crucial for poly-adenylation. The claim that the sequence is required for both termination and polyadenylation is partly incorrect. In the process of forming mature mRNA, once elongation is complete, the pre-mRNA is cleaved by an endonuclease between an AAUAAA consensus sequence and a GU-rich sequence. This cleavage occurs downstream of the AAUAAA signal and is separate from the actual termination of transcription, which is a process involving RNA polymerase II and other termination factors.
Following cleavage, poly-A polymerase adds a string of about 200 adenine (A) residues to the 3' end of the RNA, forming the poly-A tail. This poly-A tail is important for several reasons: it protects the mRNA from degradation, assists in its export from the nucleus, and influences the stability and translation efficiency in the cytoplasm.
Therefore, while the AAUAAA sequence is essential for polyadenylation, the termination of transcription is controlled by different mechanisms that recognize the end of the coding sequence, leading the transcription machinery to stop synthesizing RNA.