SELEX is a technology for the identification of high affinity oligonuc
leotide ligands. Large libraries of random sequence single-stranded ol
igonucleotides, whether RNA or DNA, can be thought of conformationally
not as short strings but rather as sequence dependent folded structur
es with high degrees of molecular rigidity in solution. This conformat
ional complexity means that such a library is a source of high affinit
y ligands for a surprising variety of molecular targets, including nuc
leic acid binding proteins such as polymerases and transcription facto
rs, non-nucleic acid binding proteins such as cytokins and growth fact
ors, as well as small organic molecules such as ATP and theophylline.
The range of applications of this technology for new discovery extends
from basic research reagents to the identification of novel diagnosti
c and therapeutic reagents. Examples of these applications are describ
ed along with a discussion of underlying principles and future develop
ments expected to further the utility of SELEX.