A novel gene expression pathway regulated by nuclear phosphoinositides

Star-PAP is a recently identified nuclear speckle localized non-canonical poly(A) polymerase that has a functional interaction with PIPKIα, and whose activity is modulated by the PIPKIα product, PI4,5P₂. Similar to other poly(A) polymerases, such as the canonical PAPα and the non-canonical GLD2 PAP, Star-PAP resides in a large complex of proteins involved in the 3′ end formation of mRNAs (Fig. 4). The Star-PAP complex shares components with the canonical PAPα complex though it contains unique associated proteins such as PIPKIα and CKIα. The Star-PAP complex assembles into a highly stable 3′ end processing machine upon oxidative stress induction. This assembled complex shows enhanced enzyme activity and hypersensitivity to exogenous PI4,5P₂, implying that an activated Star-PAP is distinctly modified and/or contains unique factors as compared to Star-PAP purified from resting cells.