The RNA guanylyltransferases from S. cerevisiae (Ceg1), vaccinia virus (D1R), Chlorella virus (A103R), and human (HCE) were expressed and purified as described before [24, 25, 30, 31] . The ATP-dependent ligase DNA ligase from Chlorella virus (ChVLig) was also expressed and purified as described previously [32] .