| Summary: | 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-t6A-A-C-C-C-A-G-A-G-m7G-U-C-G-G-U-A-G-A- Ψ -C-G-m1A-A-A-C-U-A-C-U-C-U-C-U-G-C-U-A-C-C-A OH by using post-labeling methods recently developed. The nucleotide sequence was very similar to that of mammalian tRNA i Met except for changes in six bases and three modifications: C16 U55, D47 and m5C48 are replaced by U16, Ψ 55 and unmodified U47 and C48 respectively. A50-U64 and G52-C62 base pairs of mammalian tRNA i Met are reversed in Euphausia tRNA i Met. In addition, the G 49 -C 65 pair of the former is replaced by a less stable G 49 pair in Euphausia tRNA i The sequence homology was compared between Euphausia tRNA i Met and over ten different species of eucaryotic tRNA i Met so far sequenced. The melting temperature of Euphausia tRNA i Met was 72.5°C, which is 4.2°C and 8.3°C lower than those of rat liver and yeast tRNA i Met, respectively. The origin of the thermal instability of Euphausia tRNA i Met is discussed in comparison of its secondary structure compared with those of other eucaryotic tRNA i Met's.
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