gal4 bait and pB42ad combination?

Ashok Aiyar aiyar at
Wed Jan 28 10:08:11 EST 1998

On 28 Jan 1998 04:51:56 -0800,
Jessie Theuns (theuns at wrote:

>has anybody tried to perform a two-hybrid screen using a GAL4 bait construct
>and a cDNA library cloned in pB42AD (the LexA prey plasmid)?

I think that it would be difficult to use GAL-DBD-bait constructs as
bait for cDNA libraries constructed in pB42AD.  

I believe that the GAL1 promoter is used to express the B42-cDNA 
fusion protein in pB42AD.  Thus to ensure expression of the library fusion
proteins, the transformed strain has to be be GAL4-positive and be grown
in the presence of galactose (to overcome repression).

The endogenous wild-type GAL4 protein will likely compete with the 
GAL4-DBD-bait construct for binding GAL4 sites upstream of the reporter.
Further it will activate the reporter in the absence of any library

Ashok Aiyar, Ph.D.
McArdle Laboratory for Cancer Research
aiyar at

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