U1A polyadenylation inhibition element (PIE)

The U1A polyadenylation inhibition element (PIE) is an RNA element which is responsible for the regulation of the length of the polyA tail of the U1A protein pre-mRNA. The PIE is located in the U1A mRNA 3' UTR. PIE adopts a U-shaped structure, with binding sites for a single U1A protein at each bend and when complexed with the two proteins it blocks activity of poly(A) polymerase (PAP), and inhibits its activity.