protein stability

[Barry Panaretou]

I have tried to overxpress a yeast protein (in yeast) - but I can't
detect the overexpresed protein. I can't even detect the native
protein after I've epitope tagged it - but I know its there as the ORF
is essential.
 I'm sure I've read about certain proteins in complexes which cannot
be overexpresed - because the partner protein keeps the protein in
question stable (extra protein just gets degraded). Can anyone provide
any examples of this?