Expanding the Genetic Code
Scientists in Japan have used mass spectrometry to show that an unnatural base pair in messenger RNA can incorporate new amino acids into proteins.
The scientists developed an unnatural base pair of 2-amino-6-(2-thienyl)purine (denoted by s) and pyridin-2-one (denoted by y) to expand the genetic code. The ribonucleoside triphosphate of y was site-specifically incorporated into RNA, opposite s in a template. The RNA was then translated in the bacteria Escherichia coli. The codon containing the y base (yAG) was recognized by the anticodon of a transfer RNA (tRNA) variant, which had been enzymatically aminoacylated with an unnatural amino acid, 3-chlorotyrosine. Site-specific incorporation of 3-chlorotyrosine into the translated protein was confirmed by liquid chromatography-mass spectrometry (LC-MS) in conjunction with tandem (MS/MS) mass spectrometry of the products.
The development of an unnatural base that can be specifically incorporated into RNA by polymerases would contribute to the synthesis of new proteins to assist in the development of new biological drugs and treatments.
The article appears in the February 2002 issue of the journal Nature Biotechnology (Volume 20 Number 2 pp 177 - 182).