Recorded: 08 May 2012
Restrictor Enzymes – Experiment
Okay, I used, first of all, I did an absolutely crazy experiment, in actually loading my phage, growing it in the modified host, such that it had a lot of radioactive p32 in the DNA. And it was a method which other people had developed, so called “suicide”. If you stored that DNA away during the months or so, the half-life of p32 is two weeks, then you get the slow decay of p32, and that kills the DNA. So, I could take that very hot preparation of phage, grow it just for one cycle in a non-modifying host, and storing that lysate away, and assaying every day on modifying, non-modifying hosts. And, of course the majority was not having any parental DNA and it grew perfectly well on the non-modifying host, non-restricting host. But on the restricting host originally I had about one percent, and from day to day this went down, and if it was semi-conservative it was half the rate of decay than in the conservative rate. So, that was obvious, but then I, to make absolutely clear, I repeated the same experiment, not with radioactivity, but with buoyant density, using that method which in fact Meselson and Stahl had successfully applied before, and the result was just the same.
Werner Arber, (born June 3, 1929, Gränichen, Switz.), Swiss microbiologist, corecipient with Daniel Nathans and Hamilton Othanel Smith of the United States of the Nobel Prize for Physiology or Medicine for 1978. All three were cited for their work in molecular genetics, specifically the discovery and application of enzymes that break the giant molecules of deoxyribonucleic acid (DNA) into manageable pieces, small enough to be separated for individual study but large enough to retain bits of the genetic information inherent in the sequence of units that make up the original substance.
Arber studied at the Swiss Federal Institute of Technology in Zürich, the University of Geneva, and the University of Southern California. He served on the faculty at Geneva from 1960 to 1970, when he became professor of microbiology at the University of Basel.
During the late 1950s and early ’60s Arber and several others extended the work of an earlier Nobel laureate, Salvador Luria, who had observed that bacteriophages (viruses that infect bacteria) not only induce hereditary mutations in their bacterial hosts but at the same time undergo hereditary mutations themselves. Arber’s research was concentrated on the action of protective enzymes present in the bacteria, which modify the DNA of the infecting virus—e.g., the restriction enzyme, so-called for its ability to restrict the growth of the bacteriophage by cutting the molecule of its DNA to pieces.