Fig. 9. The C-terminus of PABPN1 is necessary for poly(A) polymerase binding. GST–PAP was immobilized on GST–Sepharose beads and incubated with ³⁵S-labeled PABPN1-ΔN113 and variants in which the ΔN113 mutation was combined with progressive C-terminal truncations. Labeled cytoplasmic poly(A) binding protein from Xenopus laevis was included as a negative control. Bound proteins as well as 10% of the protein input (mix1: ΔN113, ΔN113-ΔC20, ΔN113-ΔC33 and mix2: ΔN113-ΔC8, ΔN113-ΔC27, ΔN113-ΔC49) were analyzed on a 13% SDS–polyacrylamide gel.