Reagents

TE（pH 8.0）and TBE buffers as well as 6×gel loading dye Ⅲ（with bromophenol blue only，no xylene cyanol）were prepared as described11］.Lysozyme powder，proteinase K solution，and RNase，DNase-free solution，were obtained from Boehringer Mannheim.λ DNN/HindⅢ molecular weight marker（MWM）was purchased from Gibco BRL.Agarose SeaKem GOLD（FMC）was used for electrophoresis.Note that it is critical to use this particular brand of agarose to achieve sufficient separation of genomic and plasmid DNAs.(https://www.daowen.com)