Mary Edmonds first purified the enzyme responsible for creating these structures from thymus nuclei. Mtr4p and Trf4p’s opposing functions allow the TRAMP complex to non-canonically synthesize versions of these structures that target substrates for degradation. The splicing protein U1’s relative overabundance may be due to its role in suppressing signals that induce these structures at “cryptic” sites. These structures’ namesake binding protein protects them by associating with eIF4G to inhibit the action of PARN. B cells use alternative sites for adding these structures to switch from membrane-bound to secreted antibodies. After CPSF cleaves its substrate, PAP synthesizes these structures, which are later shortened over time (-5[1])in the cytoplasm, decreasing transcript stability. For 10 points, name these long strings of a single nucleotide added to the 3-prime end of pre-mRNA. (10[1])■END■