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Vladimir Svetlov vvsvetlov at utmem1.utmem.edu
Sun Oct 6 01:58:19 EST 1996

In article <32553897.50FC at lovelace.infobiogen.fr>,
namy at lovelace.infobiogen.fr wrote:

> Hi,
> I believe that we use minimal plates for 5-FOA because the 
> URA3 gene is repressed on YPD.

Funky thing though - URA3 is believed to be under nitrogen repression and
yet we add 5 g per liter of ammonium sulfate into minimal media (according
to Current Protocols in MolBiol). So I don't think nitrogen repression per
se (which is only few fold to start with) plays such a great role here. On
the other hand it has been shown that substitution of ammonia by proline
(poor nitrogen source) causes hypersensitivity to 5-FOA. But I don't
beleive anybody figured out which of the genes - URA3 or FUR4 (uracil
permease) or other potential uracil transport proteins are affected.
Somebody tried using YPD + 5-FOA and found that sensitivity is lower than
on mimimal plates but whether YPD has more uracil, nitrogen sources more
repressive than ammonia or smth. else is yet to be seen. 
And remember - we use mimimal plates instead of YPD first and foremost
because the book saz so. One has to have some faith, you know. 
Hey, if it was stupid it would not be in the book, OK?! 
Now, back to work, all of ya - stop reading this and make yourself usefull!

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