text: The RM system was first discovered by Salvatore Luria and Mary Human in 1952 and 1953. They found that a bacteriophage growing within an infected bacterium could be modified, so that upon their release and re-infection of a related bacterium the bacteriophages growth is restricted (inhibited; also described by Luria in his autobiography on pages 45 and 99 in 1984).  In 1953, Jean Weigle and Giuseppe Bertani reported similar examples of host-controlled modification using different bacteriophage system. Later work by Daisy Roulland-Dussoix and Werner Arber in 1962 and many other subsequent workers led to the understanding that restriction was due to attack and breakdown of the modified bacteriophages DNA by specific enzymes of the recipient bacteria. Further work by Hamilton O. Smith isolated HinDII, the first of the class of enzymes now known as restriction enzymes, while Daniel Nathans showed that it can be used for restriction mapping.  When these enzymes were isolated in the laboratory they could be used for controlled manipulation of DNA, thus providing the foundation for the development of genetic engineering.  Werner Arber, Daniel Nathans, and Hamilton Smith were awarded the Nobel Prize in Physiology or Medicine in 1978 for their work on restriction-modification.