HIS3

The HIS3 gene, found in the Saccharomyces cerevisiae yeast, encodes a protein called Imidazoleglycerol-phosphate dehydratase which catalyses the sixth step in histidine biosynthesis (ref: http://db.yeastgenome.org/cgi-bin/locus.pl?locus=his3).

Exploits
Mutations in Escherichia coli's analagous gene, hisB allows researchers to select only those individuals expressing the HIS3 gene included on a plasmid. The HIS3 gene is coupled to a certain promoter which can only be activated by successful binding of the relevant transcription factors. This is used in certain methods of bacterial two-hybrid screening to allow the survival of E. coli in which a desired protein-DNA or protein-protein interaction is taking place (Joung et al., 2000)

Analogous genes in other species
hisB - Escherichia coli