To eliminate RNA, 2 μL of RNase A (Invitrogen, U.K) were added and incubated at 37°C for 1 h. 20 μL of sodium acetate 3 M and 200 μL of isopropanol were added, mixed by inversion and left to precipitate at -20°C for 2 h. The mixture was centrifuged at 8000 × g for 5 min at room temperature. The supernatant was eliminated and the precipitate washed with 300 μL of 70% ethanol. The pellet was dried and dissolved in 100 μL of TE buffer (Tris-HCl 10 mM, EDTA-Na2 1 mM, pH 8.0) at 4°C.