Transcription and RNA Processing · Zoology

What is the primary role of the polyadenylation signal (AAUAAA) in eukaryotic transcripts?

  1. It marks the transcription start site of the first exon
  2. It directs cleavage and addition of the poly-A tail
  3. It serves as the spliceosome assembly site
  4. It initiates nuclear export of the mature mRNA
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Correct answer: It directs cleavage and addition of the poly-A tail

The AAUAAA polyadenylation signal is recognized by cleavage and polyadenylation specificity factor (CPSF), which cleaves the transcript 10-30 nucleotides downstream. Poly-A Polymerase then adds ~200 adenine residues to the 3' end, stabilizing the mRNA.

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