The first nucleotide sequence of an organelle transfer RNA: Chloroplastic tRNAPhe

Abstract The primary sequence of phenylalanine tRNA (tRNA Phe ) from the chloroplasts of Euglena gracilis has been determined: pG-C-U-G-G-G-A-U-A-G-C-U-C-A-G-D-U-G-Gm-U(U ∗ )-A-G-A-G-C-G-G-A-G-G-A-C-U-G-A-A-A ∗ -A-ψ-C-C-U-U-G-U-m 7 G-Py ∗ - C-A-C-C-A-G-T-ψ-C-A-A-A-U-C-U-G-G-U-U-C-C-U-A-G-C-A-C-C-A. This represents the first nucleotide sequence determined for an organelle tRNA. As do all other tRNA Phe s thus far sequenced, chloroplastic tRNA Phe contains 76 nucleotides. Both in the nature of its modified nucleotides and in its sequence (although the sequence of all known tRNA Phe s is quite similar), chloroplastic tRNA Phe more closely resembles procaryotic tRNA Phe s than it resembles those from the cytoplasm of eucaryotes. There are eight positions in the tRNA Phe molecule where nucleotides are invariant in procaryotes but differ from invariant nucleotides in eucaryotes; at five of these positions, chloroplastic tRNA Phe is similar to procaryotes. The possible evolutionary significance of this intermediate type of structure is discussed.