Correlation of gene expression and transformation frequency with the presence of an enhancing sequence in the transforming DNA.

The transformation frequency of cultured mammalian cells is increased 10- to 100-fold when certain DNA sequences are present in the transforming DNA. We wanted to determine whether enhancers, which stimulate gene expression, can cause this phenomenon. Three plasmids, each containing a galactokinase K (galK) gene, were used to transform galK- Chinese hamster cells. One plasmid has no enhancer, another has the simian virus 40 (72-base-pair repeat) enhancer, and the third has the Harvey sarcoma virus (73-base-pair repeat) enhancer. The presence of either enhancer significantly increased the appearance of GalK+ colonies. Galactokinase transient assays in this Chinese hamster strain in the presence of the same plasmids demonstrated an increase in GalK enzyme levels when either enhancer was present. These data indicate that there is a strong correlation between galK expression and transformation frequency that is dependent on the presence of an enhancer in the transforming DNA.