ABSTRACT
The introduction of a DNA sequence in an animal cell makes it possible to analyse the role of that sequence in vivo by determining the function of a gene or identifying the regulatory sequences controlling the expression of the gene. The researcher must therefore choose the most appropriate cell line for the production of a given protein or for the study that is being carried out, as well as the most suitable vector for the cell line selected. The transfer of genes may allow their transient expression from non-integrated plasmids (see Profile 38). It is also possible to select cells in which the gene transferred is integrated. Some vectors can be maintained at the autonomous episome stage (free DNA molecules in the cytoplasm). This is the case of vectors derived from virus SV40 in COS cells and those derived from the Epstein Barr virus in primate cells.
