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limited growth on SD medium

dvd at igmors.u-psud.fr dvd at igmors.u-psud.fr
Thu Nov 16 12:04:58 EST 1995

Carol Berkower (carolb at yam-suff.cc.huji.ac.il) wrote:
But it turns out that when Leucine is combined with many other amino acids
: in the (SC-) medium, it is not as effective as when it is alone or one of
: only a few additions, ie., in the SD+ medium.  In other words, if you look

Why is this?  Does the other aa block Leucine uptake or something?

I think that your observations regarding the growth defect ofa leu- mutant is
due to the fact that the nitrogen source used in the SD medium
is ammonium sulfate. The major pathway of the ammonium assimilation in yeast
is mediated by NADP-dependent glutamate dehydrogenase whose expression is
strongly decreased in the presence of leucine in external medium (you might
want to look at paper by Yuanming Hu et al, MCB, 15:52-57 (1995) on activation
of GDH1 expression by Leu3p activator). As you will see, leucine addition in
the medium slow cell growth. So, when the medium is supplemented with leucine
(I assume that your strains are leu- auxotrophe), you can observe a limited growth. Therefore,
more the external concentration of leucine is high, more the cell growth
is affected.


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