Daniel Nathans was an American microbiologist who received the Nobel Prize in Physiology or Medicine in 1978 along with Hamilton Othanel Smith of the United States and Werner Arber of Switzerland. They were awarded the prize for the discovery of ‘restriction enzymes’ which can be used to break the molecules of DNA into small manageable portions so that the characteristics can be studied better. This discovery later became the basic tool for research in genetics. Smith had isolated the bacterium called ‘Haemophilus influenzae’ earlier which was used by Nathans in the investigations he carried out in relation to the structure of the DNA of the ‘simian virus 40’ or ‘SV40’. This virus was the simplest one known for causing cancerous tumors. Nathans constructed a genetic map of the virus which helped in identifying the molecular structure of a cancer cell with the help of the ‘restriction enzymes’. He also took part in developing prenatal procedures for testing genetic diseases such as ‘sickle cell anemia’ and ‘cystic fibrosis’. He received many awards and honors for his work and was known as an outstanding mentor, teacher and researcher. He was also an able administrator and could execute his administrative work in a fair, thoughtful, deliberate and clear-headed manner.