suppressors of null alleles

linder at linder at
Mon Nov 27 10:00:59 EST 1995

Dear Netters,

here a collection of answers I received on the fllowing request:

does anybody has tried once to isolate suppressors of a null allele? To
find parallel pathways. To rescue similar proteins for the deleted

Thanks everybody for reply. Any further comment is highly appreciated.


I once suggested such a thing at a local yeast meeting......some of the 
more experienced folks thought such an idea was nonsense. As you probably 
already know, an alternative to looking for parallel pathways that could 
be used in some cases is a screen for synthetic lethals. If you want a gene

that can substitute in your null strain, overexpression libraries is 
certainly easier but......will you get the same things if you try 
reversion analysis? The reasoning for not trying to suppress the null was 
that you'd get a whole lot of things that had nothing directly to do with 
the phenotype you're trying to suppress. However, seems to me you could 
say the same thing about some synthetic lethal screens.




Dear Patrick,

there are a lot of examples for the investigation of suppressors of null 
alleles in yeast. Look at papers describing the different MAP kinase 
signalling pathways, investigations of metabolic pathways, and so on. 
This is a standard technique in yeast. A specific paper published by our 
group is in Eur J Biochem 1993, Vol. 217, 469-477: The role of the 
NAD-dependent glutamate dehydrogenase in restoring growth on glucose of a 
S. cerevisiae phosphoglucose isomerase mutant. Here we describe the 
cloning of the NAD-GDH as a multicopy suppressor of the growth defect of 
a PGI null mutant. This suppressor allows the mutant to use the pentose 
phosphate pathway for growth on glucose because it regenerates free NADP.

Best regards

Eckhard Boles


Dear Patrick,

   We've done such selections to get bypass mutations.  They can be
informative. See:
Costanzo, M. C. and T. D. Fox, 1986  Product of Saccharomyces cerevisiae
nuclear gene PET494 activates translation of a specific mitochondrial
mRNA. Mol. Cell. Biol. 6: 3694-3703.
Best regards,



We have worked with second site suppressors that suppress a swi5 null
mutation. SWI5 encodes a transcriptional activator, and thus these
suppressors are negative regulators of transcription. 
You can find some information in Stillman et al. 1994.Genetics. 136:
and Jiang and Stillman. 1992. Mol. Cell. Biol. 12: 4503-4514. 
There are a number of other examples of second site suppressors of nulls in
transcriptional activators. 


Dear Patrick,

Vytas Bankaitis has isolated suppressors of sec14ts, which also suppress
the (lethal) sec14::knockout. There are some 6 suppressors (point 
mutants or deletions) which, in combination with sec14::knockouts render 
cells viable (and without a secretion phenotype...).
Check Cleves et al. 1991, Cell 64:789-800


Sepp D. Kohlwein


Dear Patrick,

I am glad to be able to answer one of your questions after your great help
the library about a year ago. In fact, both are connected: I have isolated 
strains which are not suppressors, but synthetically lethal with a
of a small nucleolar RNA (snoRNA). I have cloned one gene (indeed, from
library!) and it is specifically involved in pre-rRNA processing, which I
screening for! The synthetic lethality must have been caused by a block in
parallel pathway in this case. Let me know when you want to know more. Hope

this helps,

best regards,

Jaap Venema

Patrick Linder
Department of medical Biochemistry
1, rue Michel Servet
1211 Geneve 4
tel +41 22 702 54 84
fax +41 22 702 55 02
linder at

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