What was Herbert Boyer's discovery in 1969?

Herbert Boyer was born in 1936 and brought up in a corner of western Pennsylvania where railroads and mines were the destiny of most young men. He completed graduate work at the University of Pittsburgh, in 1963, followed by three years of post-graduate studies at Yale. In 1966, Boyer took over assistant professorship at the University of California at San Francisco. By 1969, he performed studies on a couple of restriction enzymes of the E. coli bacterium with especially useful properties. Boyer observed that these enzymes have the capability of cutting DNA strands in a particular fashion, which left what has became known as ‘sticky ends’ on the strands. These clipped ends made pasting together pieces of DNA a precise exercise.. This breakthrough was the basis upon which the discipline of biotechnology was founded.