DNA Transformation of Mammalian Cells

The manipulation of gene sequences between cells is a fundamental technique in genetics. Mammalian cells will take up and express genes when they are exposed to either metaphase chromosomes or naked genomic or recombinant DNA. In each case the uptake and expression is enhanced by the formation of a DNA-calcium phosphate precipitate (1 ,2 ). Alternatively, cloned recombinant DNA sequences may be introduced directly into mammalian cells by fusion with bacterial protoplasts containing recombinant plasmids (3 ) or by microinjection of purified DNA directly into the cell’s nucleus (4 ). In many cases the transforming DNA is stably expressed, and consequently alters the genotype of the recipient cell. Since long-term transformation is a relatively rare event, identification of this altered genotype requires the use of genes coding for selectable functions or for proteins easily assayable by single cell antibody or related techniques.