The prize is awarded for John's work demonstrating that mature cells can be reprogrammed to become pluripotent. John showed in 1962 that single frog nuclei transplanted into enucleated eggs could give rise to an entire animal.
John shares the prize with Shinya Yamanaka, who discovered more than 40 years later that intact mature cells in mice could be reprogrammed to become immature stem cells.
John is of course a member of this Department. He worked in the labs just above the whale for six years before moving to what is now the Gurdon Institute.
Further information can be found at http://www.nobelprize.org/nobel_prizes/medicine/laureates/2012/press.html