For the construction of pGEX-epi and pGEX-syn, the oligonucleotides GEXfw and GEXrev (Table 1) were used to introduce an XbaI and NsiI site into plasmid pGEX4T-2 (GE Healthcare, Chalfont St Giles, UK), yielding pGEX-MS. tbage and tneub were inserted into pGEX-MS via XbaI/NsiI digestion to yield the plasmids pGEX-epi and pGEX-syn.