AMINOACYLATION OF RNA MINIHELICES - IMPLICATIONS FOR TRANSFER-RNA SYNTHETASE STRUCTURAL DESIGN AND EVOLUTION

The genetic code is based on the aminoacylation of tRNA with amino aci ds catalyzed by the aminoacyl-tRNA synthetases. The synthetases are co nstructed from discrete domains and all synthetases possess a core cat alytic domain that catalyzes amino acid activation, binds the acceptor stem of tRNA, and transfers the amino acid to tRNA. Fused to the core domain are additional domains that mediate RNA interactions distal to the acceptor stem. Several synthetases catalyze the aminoacylation of RNA oligonucleotide substrates that recreate only the tRNA acceptor s tems. In one case, a relatively small catalytic domain catalyzes the a minoacylation of these substrates independent of the rest of the prote in. Thus, the active site domain may represent a primordial synthetase in which polypeptide insertions that mediate RNA acceptor stem intera ctions are tightly integrated with determinants for aminoacyl adenylat e synthesis. The relationship between nucleotide sequences in small RN A oligonucleotides and the specific amino acids that are attached to t hese oligonucleotides could constitute a second genetic code.