The binding of complementary oligoribonucleotides to yeast initiator Transfer RNA

Oligoribonucleotide binding to baker's yeast initiator tRNA was measured by equilibrium dialysis in order to determine which regions of the tRNA were free to bind complementary oligomers and which were involved in secondary and tertiary structure. Association constants of trinucleoside diphosphates and tetranucleoside triphophates complementary to the single-stranded regions of the cloverleaf structure of yeast tRNAfMet were measured at o degrees in 1.0 M NaCl, and 0.01 M MgCl2. The only regions of the tRNA whose complementary oligomers bound to the tRNA were the amino acid acceptor end and the five nucleotides at the 5' end of the anticodon loop. These results differ from those for the other tRNAs studied by this technique; usually oligomers complementary to the dihydrouracil loop bind to the tRNA. The sequence of yeast tRNAfMet and other eucaryotic initiators is unusual. The "TpsiC loop" contains the sequence A-U-C instead of T-psi-C, yet the binding pattern to the THE TpsiC LOOP IS LIKE THAT FOR OTHER TRNAs; no oligomers bind.