During early development (left), the amount of PABPC (grey) is limiting. As a result, most of the PABPC available binds to messenger RNAs (mRNAs; orange) with longer poly(A) tails, which helps ribosomes (light green) to translate these molecules more efficiently via improved recruitment of translation initiation factors (dark green). In mature cells (right), the concentration of PABPC is greatly increased, allowing it to bind indiscriminately to all poly(A) tails (blue). As other factors are present to regulate translation efficiency, the importance of PABPC in improving translation is reduced. Instead, PABPC protects mRNAs from degradation, particularly those with shorter poly(A) tails, by outcompeting decay factors (red) for binding sites on the poly(A) tail.
Image credit: Terence Tang, figure created using biorender.com.