- Transfection of eukaryotic cells is the acquisition of new genetic markers by incorporation of added DNA.
- DNA can be used to introduce new genetic features into animal cells or whole animals.
- In some viruses, the genetic material is RNA.
When DNA is added to populations of single eukaryotic cells growing in culture, the nucleic acid enters the cells, and in some of them results in the production of new proteins. When a purified DNA is used, its incorporation leads to the production of a particular protein (Pellicer et al., 1978). Figure 1.6 depicts one of the standard systems.
Although for historical reasons these experiments are described as transfection when performed with eukaryotic cells, they are a direct counterpart to bacterial transformation. The DNA that is introduced into the recipient cell becomes part of its genetic material, and is inherited in the same way as any other part. Its expression confers a new trait upon the cells (synthesis of thymidine kinase in the example of the figure). At first, these experiments were successful only with individual cells adapted to grow in a culture medium. Since then, however, DNA has been introduced into mouse eggs by microinjection; and it may become a stable part of the genetic material of the mouse.
Such experiments show directly not only that DNA is the genetic material in eukaryotes, but also that it can be transferred between different species and yet remain functional.
The genetic material of all known organisms and many viruses is DNA. However, some viruses use an alternative type of nucleic acid, ribonucleic acid (RNA), as the genetic material. The general principle of the nature of the genetic material, then, is that it is always nucleic acid; in fact, it is DNA except in the RNA viruses.