Renato Dulbecco, an Italian-born virologist who shared the 1975 Nobel Prize for medicine or physiology for providing crucial early discoveries into the genetic nature of cancer, died Feb. 19 at his home in La Jolla, Calif. He was four days shy of his 98th birthday.

The death from undisclosed causes was announced by the Salk Institute for Biological Studies, the La Jolla-based research center where Dr. Dulbecco had been a founding fellow in 1963 and later president.

In a career spanning seven decades, Dr. Dulbecco was a medical officer in the Italian army during World War II and then served with anti-German partisan forces. Focusing on scientific research after the war, he contributed to seminal advances in virology that culminated in his Nobel Prize.

One of Dr. Dulbecco’s most celebrated post-Nobel contributions was a paper he wrote for the journal Science in 1986 that advocated the complete sequencing of the human genome.

It was a bold idea at a time when many scientists were content to look at the specific genes related to their subfields. But Dr. Dulbecco foresaw the need to unravel the human genome as a prerequisite to understanding the nature of cancer.

Renato Dulbecco’s work advanced the understanding of how viruses work within cells. (Courtesy of The Salk Institute for Biological Studies)

His paper was credited with helping spark the federally funded Human Genome Project, which began in 1990 under his former colleague, James Watson, and was completed in 2003.

As a young scientist at the California Institute of Technology, Dr. Dulbecco set the groundwork for his later research by developing the innovative “plaque technique” to see viruses in action at the cellular level.

The technique allowed researchers to look at a culture sample and count the plaques, or clear spots, showing where the viruses had killed the host cells. This work — done in collaboration with biologist Marguerite Vogt — was widely credited with helping transform animal virology from a descriptive to a quantitative science.

In trying to understand the forces by which viruses infect cells and then propagate, Dr. Dulbecco built on seminal work in the early 20th century by Peyton Rous and other top scientists.

Starting at Caltech and later at the Salk Institute, Dr. Dulbecco worked with mouse cells to investigate the methods by which tumor viruses invade normal cells and seize control of their genetic structure.

His studies on mice explored two key phases of the virus’s life cycle. He showed how the genetic material of the polyoma virus can make more copies of itself and ultimately kill the cell or, more treacherously, become a stable part of that cell and cause it to proliferate, ultimately forming a tumor.

Tony Hunter, a molecular and cell biologist who now directs the Salk Institute Cancer Center, said Dr. Dulbecco made significant discoveries in the early days of tumor virology.

Previously, Hunter said, scientists viewed the interaction of a tumor virus and cell like a “hit-and-run” accident in which the effect was clear but the causes were not.

Dr. Dulbecco’s research “provided genetic evidence that the virus became part of the genome in the cancer cell,” Hunter said.

Dr. Dulbecco shared the Nobel with biologist David Baltimore, then of the Massachusetts Institute of Technology, and cancer researcher Howard M. Temin of the University of Wisconsin for what the Nobel committee termed “their discoveries concerning the interaction between tumor viruses and the genetic material of the cell.”

Temin, who died in 1994, had studied under Dr. Dulbecco at Caltech. He and Baltimore conducted breakthrough research on how some viruses carry their genetic information in ribonucleic acid, or RNA.

Dr. Dulbecco’s work had a profound impact on cancer and genetic research, fields in which he continued working for years to come. From 1972 to 1977, he worked at the Imperial Cancer Research Fund laboratories in London.

Dr. Dulbecco was president of the Salk Institute from 1988 to 1992, after which he helped organize a short-lived genome project in Italy.

Renato Dulbecco was born Feb. 22, 1914, in Catanzaro, a town in southern Italy. His father, a civil engineer, resettled the family in the northwestern community of Imperia.

At 16, he entered the University of Turin and befriended two other precocious students and future Nobel laureates: Salvador Luria, a microbiologist, and Rita Levi-Montalcini, a neurologist who is now 102.

Dr. Dulbecco received his doctorate of medicine in 1936 and joined the Italian army.

He was seriously wounded in the Soviet Union in 1942 and came home. He subsequently became a physician for local partisan fighters during the German occupation after Italy left the Axis camp.

In 1947, Dr. Dulbecco joined Luria at Indiana University and shared lab space with Watson, who went on to win a Nobel for co-discovering the structure of DNA.

Dr. Dulbecco was recruited to Caltech in 1949 and developed a research specialty in animal virology after a wealthy donor gave the school funding in that area.

He became a U.S. citizen in 1953.

In addition to the Nobel, Dr. Dulbecco received the prestigious Albert Lasker Basic Medical Research Award in 1964 for his work on cancer cells.

Dr. Dulbecco was a classically trained pianist. When he retired from the Salk Institute at 92, he said he would spend his days performing opera.

Dr. Dulbecco’s first marriage, to Giuseppina Salvo, ended in divorce. In 1963, he married Maureen Muir.

Besides his wife, of La Jolla, survivors include a daughter from his first marriage, Maria; a daughter from his second marriage, Fiona; a brother; and four grandchildren. A son from his first marriage, Peter, died in 1984.