how low can you go (nucl. acids pellets)?

suter at VAX.MPIZ-KOELN.MPG.d400.de suter at VAX.MPIZ-KOELN.MPG.d400.de
Mon Mar 21 04:28:53 EST 1994


Jim Hutchins replied to:
+ <2md9fd$qi7 at lastactionhero.rs.itd.umich.edu>
+davidlee at whitman.ccs.itd.umich.edu (David Sang-shin Lee) writes:
+>
+>I was wondering....When precipitating DNA or RNA, how little nucleic acid 
+>can you have before the pellet (after centrifugation) becomes so small 
+>it's invisible?
+>
+I have never systematically studied this, but I do know that my wife and
+I call these invisible entities "faith pellets" :-)
+I hate faith pellets; I use tRNA or glycogen whenever possible, but there
+are many, many situations where these coprecipitants cannot be used.

the problem is, that if DNA and RNA are very pure, they *ARE* invisible !
good nucleic acid looks like a glassy gel, only visible after the ethanol
is poored off. However, this kind of prep is rather seldom, my DNA preps 
usually contains enough protein and salt to result in the 'normal' white 
pellet (since this is what most of us have been using over the years, it
seems to work just as well). 
Thus it is difficult to answer your question. However, taking the average
protein contamination into account, i would say 0.1-1 microgram is still
visible.

by the way, i never add carrier to my precipitations. i have a lot of faith.

cheers,
clemens



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