Practical consequences of restriction site symmetry

Because of the palindromic character of most 6-bp restriction sites, filling-in and ligation of the protruding ends create symmetric sequences which include new 6-bp restriction sites. The old site is, in most cases, lost. After cleavage at the new palindromic site and removal of the protruding ends, a new center of symmetry is created which is often part of yet another 6-bp restriction site. A compilation of potential and available sites as presented should prove useful in genetic engineering.