Precision Editing of DNA

"Precision editing of DNA":

Scientists at the Massachusetts Institute of Technology and Rockefeller and Harvard universities have found a new method of editing DNA with great precision. This and another new technique mean that scientists can now go into a cell, find a particular sequence in the genome and change that sequence by a single letter.

Just to get your mind around this feat, imagine taking about 5,000 different novels and reprinting them in normal font size on 23 very long cotton ribbons. Since each word takes up about half an inch, the ribbons, placed end to end, would stretch for roughly three million miles-120 times around the world. But to be a bit more realistic, twist and tangle the ribbons so much that they only go around the planet once.

One of the books written on your ribbons is "A Tale of Two Cities," but you don't even know which ribbon it is on, let alone where on that ribbon. Your task is to find the clauses "It was the beast of times, it was the worst of times" and correct the misprint...