Hanafusa found the viruses reacquired the missing gene, an oncogene, from the cells' normal genetic material. The experiments also demonstrated that the viruses used the oncogene to produce tumors. Specifically, the oncogene inappropriately stimulated normal cell genes to overproduce their protein products. In these experiments, Hanafusa used the Rous sarcoma virus, named for its discoverer Peyton Rous, M.D., a Rockefeller scientist and Nobel laureate. Hanafusa's current research focuses on the structure and function of oncogenes, the proteins they make and how these genes regulate other genes in a cell.
Some oncogene proteins are enzymes that regulate basic cell functions.
His group analyzes the biochemical properties of such enzymes and how they influence cell growth and metabolism. Recently, one of these studies led to the discovery of particular protein domains, named SH2 and SH3, which play pivotal roles in protein interactions related to cell growth. Understanding the cell functions of oncogenes is key to elucidating the processes involved in cancer. He received his bachelor of science degree in 1953 and a doctoral degree in biochemistry in 1960, both from Osaka University in Japan. As a research associate at Osaka University's Research Institute for Microbial Diseases between 1958 and 1961, Hanafusa studied poxviruses.