Letters to Nature

Nature 410, 715-718 (5 April 2001) | doi:10.1038/35070613; Received 21 September 2000; Accepted 16 January 2001

Functional proteins from a random-sequence library

Anthony D. Keefe & Jack W. Szostak

  1. Howard Hughes Medical Institute, and Department of Molecular Biology, Massachusetts General Hospital, Boston, Massachusetts 02114, USA

Correspondence to: Jack W. Szostak Correspondence and requests for materials should be addressed to J.W.S. (e-mail: Email: szostak@molbio.mgh.harvard.edu). The DNA sequences encoding the consensus protein sequences of families A, B, C, D, 18predom and clone 18-19 have been deposited in GenBank under accession codes AF306524 to AF306529, respectively.

Functional primordial proteins presumably originated from random sequences, but it is not known how frequently functional, or even folded, proteins occur in collections of random sequences. Here we have used in vitro selection of messenger RNA displayed proteins, in which each protein is covalently linked through its carboxy terminus to the 3' end of its encoding mRNA1, to sample a large number of distinct random sequences. Starting from a library of 6 times 1012 proteins each containing 80 contiguous random amino acids, we selected functional proteins by enriching for those that bind to ATP. This selection yielded four new ATP-binding proteins that appear to be unrelated to each other or to anything found in the current databases of biological proteins. The frequency of occurrence of functional proteins in random-sequence libraries appears to be similar to that observed for equivalent RNA libraries2, 3.