I'm having difficulty extracting DNA (160 bp) from a PAGE gel. After cutting the DNA band from the gel, I centrifuged it by passing it through small holes made in a tube. I then left the gel in soaking buffer (Tris, EDTA, and 0.3 M NaCl) overnight at room temperature. The following day, I centrifuged and added one volume of isopropanol (at room temperature) to the supernatant. I incubated it at 30°C for 30 minutes and then centrifuged it for 30 minutes at 4°C.

At this point, I encountered the following problems:

1) No visible pellet formed.

2) The DNA is radiolabeled, so I can easily detect its location using a detector. When I took the first 200 µL of soaking buffer and checked them, I detected a very high signal of radioactivity. The same result occurred with the remaining buffer (up to a total of 1.3 mL), indicating that the DNA remained in solution and did not precipitate.

3) I tried increasing the NaCl concentration to 1 M and centrifuged again for 30 minutes, but the DNA still did not precipitate.

Where could I have gone wrong? Any suggestions?