Microbiology Procedure

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Cohesive End Method

	Cohesive End Method The work of Boyer and Cohen and their associates opened up a new way for combining different DNA species. Breaks introduced by restriction enzymes on the two strands of DNA may be opposite one another, or may be separated by several nucleotides. In the latter case sticky mortise and tenon single stranded ends are automatically produced.
This eliminates the necessity of creating mortised ends by terminal transferase action. The endonuclease EcoRI isolated in Boyer's laboratory produced breaks, with single stranded complementary ends. The unpaired nucleotides may be 2-5 nucleotides in length. Cohen opted for plasmids instead of phages as vehicles for introducing new DNA.
If a segment of DNA is removed by the successive action of two different restriction enzymes at two different points, the cohesive ends formed are different. Only a fragment of DNA with two correspondingly complementary ends can be inserted in the gap, and then too only in a unique orientation.

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