The Second Ingredient: Restriction Endonuclease Eco R1
In late 1972, several different methods were available for joining together fragments of DNA outside of cells.
Blunt ended DNA fragments could be linked together by an enzyme, DNA ligase, encoded by a gene of a bacterial virus. This had been shown by Gobin Khorana and his colleagues in 1970. Chemically synthesized DNA fragments, having complimentary projecting ends to hold them in the proper position for joining had also been linked together by Khorana.
Moreover Paul Berg and his colleagues, Peter Loban and Dale Kaiser had joined DNA fragments by attaching strings of complimentary nucleotides to them biochemically, thus eliminating the need to laboriously add the nucleotides one at a time by chemical synthesis.
As it turned out, however, the first genetic engineering experiments used still another approach, one that was different from and much simpler than these methods of DNA joining. It depended on the special properties of restriction endonucleases, enzymes that can recognize specific sequences of nucleotides on DNA, these sequences in this instance GAATTC and on the opposite strand CTTAAC, cut the DNA where these nucleotide sequences occur.
  
|
Winding Your Way Through DNA Resource Book Index
