The first nucleotide sequence of an organelle transfer RNA: chloroplastic tRNAphe.

The primary sequence of phenylalanine tRNA (tRNAphe) 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-PSI-C-C-U-U-G-U-m7G-Py-C-A-C-C-A-G-T-psi-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 tRNAPhes thus far sequenced, chloroplastic tRNAPhe contains 76 nucleotides. Both in the nature of its modified nucleotides and in its sequence (although the sequence of all known tRNAPhes is quite similar), chloroplastic tRNAPhe more closely resembles procaryotic tRNAPhes than it resembles those from the cytoplasm of eucaryotes. There are eight positions in the tRNAPhe molecule where nucleotides are invariant in procaryotes but differ from invariant nucleotides in eucaryotes; at five of these positions, chloroplastic tRNAPhe is similar to procaryotes. The possible evolutionary significance of this intermediate type of structure is discussed.