Washington: Pioneering Indian American biochemist, Har Gobind Khorana, who won the 1968 Nobel Prize for medicine, died of natural causes in Concord, Massachusetts. Khorana, 89, who was MIT's Alfred P Sloan Professor of Biology and Chemistry emeritus, died earlier this week.

He won the Nobel Prize in 1968, sharing it with two others, for unravelling the nucleotide sequence of RNA and deciphering the genetic code. He was then with the University of Wisconsin (UW).

He is survived by his daughter, Julia, and son, Dave.

Born in 1922, in a small village called Raipur in Punjab, which is now in Pakistan, Khorana is known as a scientist who revolutionised biochemistry with his pioneering work in DNA chemistry.

"The work that he did in Wisconsin from 1960 to 1970 continues to propel new scientific discoveries and major advances," said Aseem Ansari, professor of biochemistry at the University of Wisconsin-Madison where Khorana taught and did research from 1960 to 1970 before moving to the Massachusetts Institute of Technology (MIT).

It was at Wisconsin that Khorana along with his colleagues worked out mechanisms of RNA codes for the synthesis of proteins, which won him the Nobel Prize.

He shared the prize with Robert Holley of Cornell University and Marshall Nirenberg of the National Institutes of Health. Khorana was among the pioneers of the now-familiar series of three-nucleotide codons that signal to the cell which amino acids to use in building proteins —- for example, uracil-cytosine-uracil, or UCU, codes for the amino acid serine, while CUC codes for leucine, MIT said in a statement.

"Gobind was a brilliant, path-breaking scientist, a wise and considerate colleague, and a dear friend to many of us at MIT," said Chris Kaiser, MacVicar Professor of Biology and head of the Department of Biology, in an email announcing the news.

In a statement released by MIT, Khorana's daughter, Julia Khorana, said her father loved mentoring young scientists. "Even while doing all this research, he was always really interested in education, in students and young people," she said.

"After he retired, students would come to visit and he loved to talk to them about the work they were doing. He was very loyal to them, and they were very loyal to him, too," she said.

Inspired by Khorana's story in 2007, UW-Madison faculty members Ansari and Ken Shapiro established the Khorana Scholars Programme to enable the exchange of top students between select Indian research institutions and the UW-Madison.

The programme has recently expanded to include students from other Midwestern universities as well as MIT, Harvard and some West Coast schools, the university said in a statement.

The programme also sends Wisconsin agricultural scientists to India to assist in entrepreneurial efforts to improve economic stability and food security in poor rural areas.

"There's no more appropriate way to honour Khorana," Ansari said in a statement. "He served as an icon for why international programmes are so important. He personified the Wisconsin Idea, the idea of knowledge without boundaries. Here was a man who came from a poor rural Indian family, working in Wisconsin, making a contribution that changed the course of science."

Khorana, in an autobiographical note after getting the Nobel Prize, wrote, "Although poor, my father was dedicated to educating his children and we were practically the only literate family in the village inhabited by about 100 people."

According to his biography issued by the MIT, Khorana attended high school in the nearby city of Multan before enrolling in Punjab University, where he received his bachelor's degree in 1943 and master's in 1945, both in chemistry and biochemistry.

Upon graduating, he received a fellowship from the Indian government to study at the University of Liverpool in the UK, where he received his PhD in 1948.

Khorana did postdoctoral work at Switzerland's Federal Institute of Technology, where he met his wife, the late Esther Elizabeth Sibler.

After returning to the UK for another postdoc position in Cambridge, Khorana and his wife created a new home together in Vancouver, Canada, where he took a job at the British Columbia Research Council in 1952.

Khorana stayed in Vancouver for eight years.

In 1960, he went to the University of Wisconsin at Madison, where he became co-director of the Institute for Enzyme Research.