- A: alpha arrays
- X: N-terminal helical domain in Poxvirus poly(A) polymerase catalytic subunit
- H: N-terminal helical domain in Poxvirus poly(A) polymerase catalytic subunit
- T: N-terminal helical domain in Poxvirus poly(A) polymerase catalytic subunit
- F: Pox_polyA_pol_N