I have tried using various methods, but still no results.
A method that can be followed in institutional level.
If I understand you correctly you have not been successful in recovering the DNA from your cell.
I would recommend to prepare a lysis buffer containing : 20mM tris pH 7.5, 150 mM NaCl, 1% Triton X100, 1mM MgCl2) , scrap your cells in this buffer (1ml for 20 million cells) incubate for 10' (Vortex) and centrifuge at 700 x g for 5'. The pellet contains the chromatin. Resuspend the pellet in a PK buffer 200µl (30mM tris pH 7.5, 2mM CaCl2, 0.2% SDS) then add some Proteinase K (PK) and incubate for 45' at 37°C. During this step you will digest all the protein associated with the DNA which will result in fairly pure DNA. You can then precipitate with ethanol overnight and resuspend in water. The DNA will be good enough for PCR.
To add a similar but alternative method to the above, you could also perform cell lysis in a TNES buffer: 50mM Tris pH 7.5, 0.4M NaCl, 100mM EDTA, 0.5% SDS. Use proteinase K as suggested above. Then precipitate proteins using an equal volume of 5M ammonium acetate (final concentration 2.5M) OR 1/10th volume 3M sodium acetate. Mix until it goes fluffy, spin down, remove supernatant and ethanol precipitate the DNA.
I have had very good results with this method.
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