Glimpses of an RNA World

[Rcjohnsen]

Glimpses of an RNA World

Biochemists have long speculated that life may have begun in an 
"RNA world," in which single-stranded ribonucleic acid (rather 
than double-stranded DNA) handled both the carrying of genetic 
information and the biochemical heavy lifting of protein synthesis.  
Three landmark studies in the 11.8.2000 issue of Science offered 
stunning new evidence for that view.  Ban et al. 
(http://www.sciencemag.org/cgi/content/short/289/5481/905) used 
x-ray crystallography to deduce the atomic structure, at a 2.4-
angstrom resolution, of the large subunit of the ribosome, the cell's 
basic protein-building factory.  Drawing on those data, Nissen et 
al. (http://www.sciencemag.org/cgi/content/short/289/5481/920) 
established that it is the subunit's two RNA molecules, and not the 
surrounding structural proteins, that actually catalyze peptide-bond 
formation and, thus, protein synthesis in the ribosome, in marked 
contrast to the traditional view in which the RNA is the structural 
element and the proteins act as the catalysts.  And Muth et al. 
(http://www.sciencemag.org/cgi/content/short/289/5481/947) 
showed that the key to the reaction lies in a single nucleotide base 
within the RNA that's present at that position in all known life -- a 
clear suggestion of a primordial RNA world.  A Perspective by T. 
R. Cech 
(http://www.sciencemag.org/cgi/content/summary/289/5481/878) 
placed these papers in the larger context of structural and 
evolutionary biology.