ABSTRACT
The two hybrid system was developed to reveal protein-protein interactions. This test is based on the fact that many proteins, including transcription factors, are composed of several independent functional domains. When these domains are physically distant, they have no biological activity. But if they are brought close to one another by non-covalent interactions, a functional protein can be reconstructed. The Gal4 protein activator of the transcription of genes for galactose metabolism in the yeast Saccharomyces cerevisiae is composed of two distinct and separable functional domains: a DNA binding domain (DBD) and a transcription activation domain (AD).
