Today, a wide spectrum of very specific plasmids is available. Some of them serve just very limited purposes and survive only in certain strains of bacteria. The signals recognized by procaryotic cells differ fundamentally from those needed by eucaryotic cells. The transfer of a bacterial plasmid into a eucaryotic cell and its expression there is thus not possible directly. The T i -plasmid is an exception.
Eucaryotic cells understand the signals preceding the synthetase genes of octopine and nopaline.
Therefore, a foreign DNA coupled in the right reading frame behind such a signal makes sense for a eucaryotic cell. Cloning is, in practice, a process consisting of several steps that leads finally to the wanted DNA-hybrid. Only those parts of the T i -plasmid that are absolutely essential for transfer into the plant and integration into the plant s genome are used. It is important that the tumor regenerates into a complete plant containing the foreign gene and that the latter is not lost during differentiation. The next challenge is meiosis, but it was principally solved.