About molecular cloning, does anyone know about extraction DNA from polyacrylamide gel?

A polyacrylamide gel is a separation matrix used in electrophoresis of biomolecules, such as proteins or DNA fragments. Traditional DNA sequencing techniques such as Maxam-Gilbert or Sanger methods used polyacrylamide gels to separate DNA fragments differing by a single base-pair in length so the sequence could be read. Most modern DNA separation methods now use agarose gels, except for particularly small DNA fragments. It is currently most often used in the field of immunology and protein analysis, often used to separate different proteins or isomers of the same protein into separate bands. These can be transferred onto a nitrocellulose or PVDF membrane to be probed with antibodies and corresponding markers, such as in a western blot.


[edit] Composition
Polyacrylamide gels are formed by polymerization of acrylamide and crosslinker N,N'-methylene bisacrylamide. Otherwise slow polymerization is greatly accelerated by free radicals released from ammonium persulfate in the presence of tetramethylethylenediamine. The density of the resulting cross-polymer lattice depends on the amount of acrylamide and the crosslinker in the reaction mix. The bigger the pores in the gel, the faster the protein or DNA molecules can move. One of the purposes of acrylamide gel is to separate protein or DNA molecules of similar molecular mass or size. Denser gels, containing for example 10-12% acrylamide, are necessary to resolve small proteins, which would otherwise run fast through gels with large pores. To resolve large proteins, one has to use gels with larger pores to allow the molecules to enter and move through the lattice.

The choice of buffer filling the acrylamide lattice depends on the molecule to be analyzed. For example, to prepare a gel for SDS-PAGE, polymerization reaction will be set up in the presence of SDS and Tris-HCl buffer, while for native PAGE the SDS will be omitted.


[edit] Resolving gels
Typically resolving gels are made in 6%, 8%, 10%, 12% or 15%. Stacking gel (5%) is poured on top of the resolving gel and a gel comb (which defines the lanes where proteins, sample buffer and ladders will be placed) is inserted.

The percentage chosen depends on the size of the protein that one wishes to identify or probe in the sample. The smaller the known weight, the higher the percentage that should be used.


[edit] Recipes
The mixtures below will not polymerize until the TEMED has been added, but if stored unpolymerized for long enough, the mixture may not polymerize correctly. Standard gel size is 3"x5"x.2", and accounting for a small amount of leakage that generally occurs, each takes roughly 8mL of resolving and 2 mL of stacking gel.

To make 10 ml of a 10% (resolving) polyacrylamide mixture:

dH20                            4.0 ml
30% acrylamide mix              3.3 ml
1.5M Tris pH8.8                 2.5 ml
10% SDS                          .1 ml
10% ammonium persulfate          .1 ml
TEMED                            .004 ml
To make 10 ml of a 5% (stacking) polyacrylamide mixture (note, the volumes are same as for above, only the Tris concentration varies):

dH20                            4.0 ml
30% acrylamide mix              3.3 ml
1.0M Tris pH6.8                 2.5 ml
10% SDS                          .1 ml
10% ammonium persulfate          .1 ml
TEMED                            .004 ml

sorry i dont really know, but a kit designed for extraction might work o.k. I'm guessing that you have tried regular high salt or phenol based methods and these have not been successful, perhaps repeating the extraction protocol on the resulting product may help.

had to laugh at the above answer, clearly has no idea but has got the hang of copy and paste!