High Quality Content by WIKIPEDIA articles! The bacterial one-hybrid (B1H) system is a method for identifying the sequence-specific target site of a DNA-binding domain. In this system, a given transcription factor (TF) is expressed as a fusion to a subunit of RNA polymerase. In parallel, a library of randomized oligonucleotides representing potential TF target sequences, is cloned into a separate vector containing the selectable genes HIS3 and URA3. If the DNA-binding domain (bait) binds a potential DNA target site (prey) in vivo, it will recruit RNA polymerase to the promoter and activate transcription of the reporter genes in that clone. The two reporter genes, HIS3 and URA3, allow for positive and negative selections, respectively. At the end of the process, positive clones are sequenced and examined with motif-finding tools in order to resolve the favoured DNA target sequence.