cDNA library question - (Mar/26/2008 )

How an indivual cDNA from a cDNA liberary can be isolated if one donot know the sequence of of the target cDNA library. I mean if some one is looking for cDNA which will encode a membrane protein which can be activated by some agonist.
If some one have a cDNA library for example of mouse brain and i know some cDNA encode some protein which is activated by drug how can i isolated that cDNA from the pool of library.

Second when you prepare cDNA library then there is concept of fractioning of cDNA library what does it mean.

there are a couple of ways to screen a library, depending on the type of library.

if you have an expression library then you can screen for your protein with an antibody (similar to western blot).

if not then, if you know the amino acid sequence of the protein or a fragment, you can develop a degenerate oligo probe with which to screen the library.