THE 2.9 ANGSTROM CRYSTAL-STRUCTURE OF THERMUS-THERMOPHILUS SERYL-TRANSFER-RNA SYNTHETASE COMPLEXED WITH TRNA(SER)

The crystal structure of Thermus thermophilus seryl-transfer RNA synth etase, a class 2 aminoacyl-tRNA synthetase, complexed with a single tR NA(Ser) molecule was solved at 2.9 Angstrom resolution. The structure revealed how insertion of conserved base G20b from the D loop into the core of the tRNA determines the orientation of the long variable arm, which is a characteristic feature of most serine specific tRNAs. On t RNA binding, the antiparallel coiled-coil domain of one subunit of the synthetase makes contacts with the variable arm and T Psi C loop of t he tRNA and directs the acceptor stem of the tRNA into the active site of the other subunit. Specificity depends principally on recognition of the shape of tRNA(Ser) through backbone contacts and secondarily on sequence specific interactions.