Chemical structure and thermal properties of initiator tRNA from Euphausia sperba in comparison with those of other eucaryotic initiator tRNAs.

The nucleotide sequence of initiator tRNA (tRNAiMet) from Euphausia sperba, which was harvested in the Antarctic Sea, was determined to be pA-G-C-A-G-A-G-U-m1G-m2G-C-G-C-A-G-U-G-G-A-A-G-C-G-U-m2G-C-U-G-G-G-C-C-C-A-U-t6 A-A-C-C-C-A-G-A-G-m7G-U-C-G-G-U-A-G-A-psi-C-G-m1A-A-A-C-U-A-C-U-C-U-C-U-G-C-U-A -C-C-AOH by using post-labeling methods recently developed. The nucleotide sequence was very similar to that of mammalian tRNAiMet except for changes in six bases and three modifications: C16, U55, D47 and m5C48 are replaced by U16, psi 55 and unmodified U47 and C48, respectively. A50-U64 and G52-C62 base pairs of mammalian tRNAiMet are reversed in Euphausia tRNAiMet. In addition, the G49-C65 pair of the former is replaced by a less stable G49-U65 pair in Euphausia tRNAiMet. The sequence homology was compared between Euphausia tRNAiMet and over ten different species of eucaryotic tRNAiMet so far sequenced. The melting temperature of Euphausia tRNAiMet was 72.5 degrees C, which is 4.2 degrees C and 8.3 degrees C lower than those of rat liver and yeast tRNAiMet's, respectively. The origin of the thermal instability of Euphausia tRNAiMet is discussed in comparison of its secondary structure compared with those of other eucaryotic tRNAiMet's.