Developed a variety of two-hybrid system is mostly based system established by Fields et al. These new systems are mainly on the reporter gene, "bait" expression vector "prey" expression vector made some improvements. One of the important improvement is the introduction of additional reporter genes HIS3 gene, such as the widely adopted. Transformed with the yeast cells of the HIS3 reporter gene HIS3 be started, only when the expression can grow on selective medium lacking histidine. HIS3 transcriptional expression of the reporter gene is activated by the "bait" and "prey" interaction. Most two-hybrid system often simultaneously use two or even three reporter genes, one of which is LacZ. After transformation the gene same activator of transcription factor binding sites in the promoter region and can therefore be the same transcription activating factor (as described above, the Gal4 protein) activation. By double or multiple choice both to improve the detection sensitivity and reduce false positives. Other improvements made for "bait" or "prey" expression vector.