End-labelling and addition of linkers

The aim of this step is simply to add an EcoKl recognition site to both ends of the pool of restriction fragments obtained from the unknown DNA. 

Aiul fragment with EcoRI sticky ends 

Whatever labelling scheme is employed the next stage is the polymerization of linker onto the ends of the fragment(s). In order to remove DNA polymerase and the restriction enzyme from the reaction mixture the most straightforward procedure is to shake with phenol (Section 4.3.6.) and precipitate the DNA from the aqueous supernatant with ethanol. After washing with ethanol and 

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