Essentially identical to the selected and amplified (protein) binding site oligonucleotide (SAAB) and target detection assay (TDA) procedures; a procedure for identification of consensus sequences of DNA to which a protein, e.g. a transcription factor, may bind. A random polynucleotide sequence is synthesised flanked by two defined sequences that will serve as templates for PCR primers; the polynucleotides are exposed to the DNA-binding protein, any complex that is formed is separated from the unliganded polynucleotides (e.g. by gel shift assay, affinity chromatography, philtre binding) and the polynucleotide of the complex is isolated and amplified by PCR; repeated recycling through the sequence of ligand formation, selection and amplification results in a preparation that is sufficiently pure to be cloned into bacteria for larger-scale production. A variant is systematic evolution of ligands by exponential enrichment (SELEX) for identification of RNA sequences, which begins with a mixture of polyribonucleotides and in each cycle produces DNA from the selected RNA-protein complex using reverse transcriptase, amplifies it by PCR, and then produces new RNA transcripts for the next round of selection. see genomic SELEX