4.2  Expression and purification of recombinant proteins
SARS-CoV nsp14 and human RNA N7-methyltransferase (hRNMT) coding sequences were cloned in fusion with a N-terminus hexa-histidine tag in Gateway® plasmids. The proteins were expressed in E. coli and purified following previously described protocols [33,39]. Vaccinia virus capping enzyme (D1/D12 complex) and mRNA Cap 2′-O-methyltransferase (VP39) were purchased (New England Biolabs).