Then, it was successively treated with 60 lL lysozyme
mixture (37 C, 60 min), 60 lL protease mixture (37 C,
30 min) and 80 lL 20% sodium dodecyl sulfate (37 C, 90 min).
The mixture was extracted using phenol–chloroform–isoamyl
alcohol (25:24:1) at 65 C for 20 min, and the supernatant was
extracted using chloroform–isoamyl alcohol (24:1). The extraction
was then mixed with 0.6 volumes of isopropanol and stored at 4 C
overnight