Direct translation from DNA to protein has been demonstrated in a cell-free system (i.e. in a test tube), using extracts from E. coli that contained ribosomes, but not intact cells. These cell fragments could synthesize proteins from single-stranded DNA templates isolated from other organisms (e.g., mouse or toad), and neomycin was found to enhance this effect. However, it was unclear whether this mechanism of translation corresponded specifically to the genetic code.