PAP Associated Domain Containing Protein 4 (PAPD4)

TUTase2 performs the guide RNA (gRNA) directed addition of U residues to single stranded (ss) mRNA. RET2 addition of U residues to the 3’ end of pre-cleaved mRNA (mRNA/gRNA duplex) is also responsible for promoting re-ligation of the cleaved mRNA substrate by RNA editing ligase 2 (REL2).

RET2 interacts with the protein MP81 (KEPA1), which also serves to couple RET2 to the REL2 ligase. The enzyme utilizes three positively charged amino acid residues for the recognition and binding of ssRNA substrates. The ribose sugar of UTPs is recognized by residues from both the N-terminal and C-terminal domains. Uridine base specificity is conveyed by base stacking interactions with Y319 along with hydrogen bonding to N277 and a coordinated water .