During this phase, nucleotide sequences are each made of the mRNA transcript to protect it from degradation that can occur outside of the nucleus. The 5’ end of a single G nucleotide is attached to the 5’ end of the transcript. This is called the 5’ cap. At the 3’ end of the transcript, a long sequence of A nucleotides are attached. This is called the poly-A tail. The 5’ cap and the poly-A tail protect the mRNA transcript from attack by enzymes in the cytoplasm called exonucleases that specifically target mRNA molecules with exposed 5’ ends.