Australian-American researcher Elizabeth Blackburn and Carol Greider and Jack Szostak of the United States won the Nobel Medicine Prize today for identifying a key molecular switch in cellular ageing.<br/><br/>The trio were honoured for the discovery of how chromosomes are protected by telomeres and the role of an<br/><br/>enzyme called telomerase in maintaining or stripping away this vital shield. The Nobel jury said it recognizes the discovery of a fundamental mechanism in the cell, a discovery that has stimulated the development of new therapeutic strategies.<br/><br/> The three told Swedish Radio they were overjoyed by the news.