3-Amino-1,2,4-triazole

3-Amino-1,2,4-triazole (3-AT) is a heterocyclic organic compound that consists of a 1,2,4-triazole substituted with an amino group.

3-AT is a competitive inhibitor of the product of the HIS3 gene, imidazoleglycerol-phosphate dehydratase. Imidazoleglycerol-phosphate dehydratase is an enzyme catalysing the sixth step of histidine production.

3-AT is also is a nonselective systemic triazole herbicide used on nonfood croplands to control annual grasses and broadleaf and aquatic weeds. It is not used on food crops because of its carcinogenic properties. As an herbicide, it is known as aminotriazole, amitrole or amitrol.

Exploits
By applying 3-AT to a bacterial cell culture which is dependent upon a plasmid containing HIS3 to produce histidine (i.e. its own HIS3 analogue is not present or nonfunctional), an increased level of HIS3 expression is required in order for the bacterial cell to survive. This has proved useful in increasing the affinity of DNA-binding domains selected in one bacterial two-hybrid technique described by Joung et al., in 2000. Since the DNA-binding domain in turn recruits RNA polymerase to the HIS3 gene, a high affinity binding will allow the bacterial cell to survive in media containing higher concentrations of 3-AT. Of course this selection process is performed using selective media, containing no histidine.

1959 cranberry contamination
On November 9, 1959, the secretary of the United States Department of Health, Education, and Welfare Arthur S. Flemming announced that some of the 1959 crop was tainted with traces of the herbicide aminotriazole. The market for cranberries collapsed and growers lost millions of dollars.