Chemical Structure and Thermal Properties of Initiator tRNA from Euphausia sperba in Comparison with Those of Other Eucaryotic Initiator tRNAs1

Abstract

The nucleotide sequence of initiator tRNA (tRNA^iMet) 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 G₄₉-C₆₅ pair of the former is replaced by a less stable G₄₉ 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.