isopropanol to precipitate DNA: how much?

[(Dave Johnston)]

Hi Zhengyang
0.8 volumes is fine, more is just wasteful. With isopropanol, if you 
freeze you tend to precipitate the salts as well so do it at room 
temperature. The other advantage is that the final volume of the 
precipitation solution is smaller, this can save you having to suballiquot 
your aqueous DNA solution prior to precipitation, use more convenient/less 
tubes etc. The disadvantage is that the DNA pelllet tends to be glass like 
and clear, rather than opaque so can be difficult to see, especially if 
your DNA is pure and the yield is small. We routinely use linear 
polyacrylamide as a carrier in isopropanol precipitated minipreps to 
make sure rthat we don't accidently loose the pellet.
DAJ

David A. Johnston
Research Fellow,
Dept of Zoology, The Natural History Museum, Cromwell Road,
South Kensington, London SW7 5BD. England
tel 0171 9389297 (from outside UK: 44 171 9389297)
fax 0171 9388754 (from outside UK: 44 171 9388754)
email daj at nhm.ac.uk