从一篇文章上抄来的: cDNA encoding 'artificial' SUMO-2 'polymers' was generated by ligating PCR products encoding DeltaN11–SUMO-2 while simultaneously digesting with restriction enzymes specific for BamHI (N-terminal site) and BglII (C- terminal site) in T4 DNA ligase buffer, 150 mM NaCl, 0.1 mg ml- 1 BSA at 22 °C for 5 h (enzymes and buffers from New England Biolabs). This created a range of cDNAs encoding DeltaN11–SUMO-2 cDNA 'monomers' and 'multimers' that were separated by agarose gel electrophoresis and individually extracted into solution. These were then ligated into the BamHI site in pHis –TEV plasmid27 which had the EcoRI restriction site mutated into a stop codon. Expression from these plasmids gives N-terminal 6His-tagged proteins containing one, two, three or four copies of DeltaN11–SUMO-2. Each SUMO-2 ' monomer' is separated from the other by Arg–Ser, which is also present at the C-terminus before the stop codon.