urban "lab" legends

suter at de.dbp.MPG.MPIZ-KOELN.VAX suter at de.dbp.MPG.MPIZ-KOELN.VAX
Mon Jul 27 06:20:16 EST 1992

dear colleagues,

Ed Rybicki writes:

< Basavareju Shankarappa writes:
<>>>>I have observed that using NaCl for pptn of DNA often results in
<>>>>precipitation of salt specially after prolonged incubation at
<>>>>-20 C.  I learnt this from my experience rather than anything.
<> Disclaimer: Of course, my grad students put their DNA into the freezer
<> to precipitate...
<Why do they do that?  So ANNOYING!!  I used to think it was because older
<protocols had it in, but I now think it's because it's the lab equivalent of an
<urban legend, and the buggers don't ever bother to go and look up methods
interesting point, about urban legends (lab legends ?). Here are a few more,
which are (in my humble opinion) either unnecessary or even counterproductive:
1. always store your 70% and 100% ethanol at -20C (main advantage: as
   soon as you open the bottle, water is sucked in, lowering your ethanol conc)
2. always hybridize in the presence of 0.1-0.5 % SDS (7% SDS is superior to
   suppress background, but we'll stick to the old protocol anyway)
3. in each ligation, use at least 1 micro liter of ligase (usually 100 fold 
   excess of enzyme, works better, eh?)
4. all southern filters should be baked at 80C...under vacuum (o.k. o.k.
   all manufacturers convince us this is only necessary for nitrocellulose,
5. DNA should be dried in the speedvac for at least 10-20 minutes (why is
   it so hard to dissolve my pellet ?)
6. NaCl is the salt of choice for ethanol precipitations (NaAc ? NH4Ac ? 
   LiCl ? LiAc ? MgAc ? lets take a look in Sambrook !)
7. library screening. always use these round NC filters that fit exactly on 
   the agar plates...even when they are 10 times more expensive than the
   square ones you can cut from a roll !
8. And the last one: HeLa cells originate from Helen Lane or Henrietta Lacks
   (whereas insiders know they were invented by Henry "hip" LaBouchette !)

did i start some new rumours ?
cheers ! clemens
----------------------------------> cut here <----------------------------------
Clemens Suter-Crazzolara, PhD
Max-Planck-Institut fuer Zuechtungsforschung
Abteilung Genetische Grundlagen der Zuechtungsforschung
Carl-von-Linne Weg 10
5000 Koeln 30
Tel. xx49-221-5062.221           fax. xx49-221-5062.213
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handling charge are not included.
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