Equipment and reagents

Glycine and sodium dodecyl sulfate (SDS) were purchased from Sigma (St. Louis, MO, USA). All restriction enzymes and ligases were obtained from New England Biolabs (Ipswich, MA, USA). Plasmid Miniprep kits and transfection kits were purchased from Tiangen (Beijing, China). All other materials were domestic or imported analytical reagents. The equipment used in this study included a high-speed, refrigerated centrifuge (Universal 16R; Hettich, Tuttlingen, Germany), an ultraviolet spectrophotometer (UVl601; Shimadzu Corp., Kyoto, Japan), a GeneGenius gel image analysis system (Synoptics Ltd., Cambridge, UK), a microelectrophoresis and transfer system (Bio-Rad Laboratories, Inc., Hercules, CA, USA).