Daniel Nathans, esteemed scientist, professor, former interim president of the university and recipient of the Nobel Prize, died in his sleep Nov. 16 from leukemia. He was 71.

Funeral services were private. The date for a memorial service will be announced soon.

University Professor of Molecular Biology and Genetics at the School of Medicine, where he was a faculty member for more than three decades, Nathans also was senior investigator of the Howard Hughes Medical Institute at Hopkins. He served as interim president of the university from June 1995 until August 1996. In addition to being awarded the Nobel Prize in 1978, Nathans was a 1993 recipient of the National Medal of Science, the nation's highest scientific award.

Interim President Daniel Nathans after receiving a surprise honorary degree at commencement, May 22, 1996. Sadako Ogata, United Nations high commissioner for refugees, is at left. Among those applauding Nathans are, middle row from the left, trustees Martin Macht, Aurelia Bolton and Randolph Bromery; rear row, trustee R. Champlin Sheridan, associate dean of Engineering Candice Dalrymple and trustee Shale Stiller.

The research for which Nathans, his colleague Hamilton O. Smith and Swiss microbiologist Werner Arber shared the Nobel Prize in physiology or medicine was a basis for much of today's genetic research at Hopkins and elsewhere. Nathans and his students used a restriction enzyme discovered by Smith as "biochemical scissors" to analyze DNA.

As the Nobel Prize committee rightly predicted, the techniques developed by Nathans in working with animal tumor viruses opened up new avenues to study the organization and expression of genes of higher animals and to solve basic problems in developmental biology. In medicine, as the committee predicted, increased knowledge made possible by his focus on genetic mechanisms has helped in the understanding, prevention and treatment of birth defects, hereditary diseases and cancer.

Restriction enzymes have allowed researchers to assemble genes in new combinations, thus giving birth to the entire field of genetic engineering and allowing development of such products as synthetic human insulin, growth hormone and interferon. The use of restriction enzymes to construct maps of the genome of viruses laid the groundwork for the present worldwide effort to map the human genome.

A molecular biologist, Nathans focused his research first on viruses that cause tumors in animals and then on cellular responses to growth factors, the mechanisms that cause cells to grow and multiply. In 1969, while Nathans was studying SV40, a virus that created cancers in apes, Smith came forward with interesting news: He had isolated a protein that could cut a piece of DNA, the material containing the "blueprint" of life.

Nathans applied the restriction enzyme to SV40 DNA and discovered that it cut the DNA in 10 distinct places, creating 11 well-defined fragments. He found ways to use this cutting to help determine where genes began and ended in SV40 DNA, and this helped him locate a gene in the virus that gives the order for production of a tumor-making protein.

Meanwhile, Nathans, Smith and Werner Arber, the Swiss scientist who first predicted the existence of restriction enzymes, woke up one morning in 1978 to the call from Sweden that so many scientists dream about. More honors for Nathans followed. In 1979 he was elected to the National Academy of Sciences and in 1985 to the American Philosophical Society; from 1990 to 1993 he served on the Presidential Council of Advisors on Science and Technology.

As a physician, Nathans understood human disease and its impact. But he kept his focus on the science. "Scientists don't do research for the prizes," he once explained to a reporter. "They do it because they enjoy discovering or understanding an important phenomenon. The greatest reward is seeing your discovery lead to some practical application, and sometimes that's hard to foresee. But I was always confident that, in the long run, the study of basic genetic mechanisms would contribute to the well-being of people everywhere."

When he was named a co-recipient of the Nobel Prize, Nathans described himself as a "pretty intense" scientist who had never so much as "fantasized" about winning a Nobel. That modest, soft-spoken intensity characterized his career. When the fanfares ended and the spotlights shut down, his colleagues insist, Nathans was always glad to go back quietly to his laboratory and do what he loved best: answer scientific questions and teach.

Swayed by his reputation for quiet, potent leadership, the trustees of the university in 1995 asked him to be interim university president while a search committee sought a permanent appointee for the job.

"It was an interesting job, being the president," Nathans later said with characteristic understatement. "If I learned anything in my first few months, it was that the president has to resolve all the disagreements that no one else can resolve."

He also was clear about why he accepted the job: "I've always considered it a privilege to be here, to lead the kind of life Hopkins has given me the opportunity to lead," he said. "It's a great feeling ... to start your own research program and be given the time, facilities and support ... and to know what comes out of it is up to you. I'd like to preserve that feeling for others. ... And that's a fair part of why I decided to take on the interim presidency."

Born Oct. 30, 1928, in Wilmington, Del., the youngest of eight children, Nathans received his bachelor of science from the University of Delaware in 1950 and earned his M.D. at Washington University School of Medicine in St. Louis in 1954. Following his residency at Columbia-Presbyterian Medical Center in New York, he served as a clinical associate at the National Cancer Institute and as a guest investigator at the Rockefeller University.

His first faculty appointment was as a Hopkins assistant professor of microbiology in 1962, and he stayed at Hopkins for the rest of his career. He became a full professor in 1967, director of the Department of Microbiology in 1972 and director of the Department of Molecular Biology and Genetics in 1981.

Nathans relaxed by reading history or literature, walking, swimming or listening to chamber music. He was married to Joanne Gomberg Nathans, a lawyer who served for years in Baltimore City's Department of Legislative Reference. They have three sons, Eli, a lawyer completing a doctorate in European history at Hopkins; Jeremy, a professor of molecular biology and genetics in the School of Medicine; and Ben, a professor of European history at the University of Pennsylvania; and six grandchildren.

The family requests that memorial contributions be sent to the School of Medicine c/o The Fund for Johns Hopkins Medicine, 1620 McElderry St., Baltimore, MD 21205; please write, "in memory of Dr. Nathans."