In 2006, researchers made cultured skin cells behave like embryonic stem cells by adding a handful of genes. But the method by which they inserted the genes - using viruses -can turn cells cancerous.rnThis year, two groups accomplished the same feat by delivering just the protein products of these genes into cells. Sheng Ding at the Scripps Research Institute in La Jolla, California, and his colleagues converted mouse embryonic fibroblasts into embryonic-like stem cells by using the bacterium Escherichia coli to engineer modified versions of the proteins that could cross the cellular and nuclear membranes.
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