Abstract
The nucleotide sequence of formylmethionine tRNA from an extreme thermophile, Thermus thermophilus HB8, was determined by a combination of classical methods using unlabeled samples to determine the sequences of the oligonucleotides of RNase T1 and RNase A digests and a rapid sequencing gel technique using 5'-32P labeled samples to determine overlapping sequences. Formylmethionine tRNA from T. thermophilus is composed of two species, tRNAMetf1 and tRNAMetf2. Their nucleotide sequences are almost identical, and are also almost identical with that of E. coli tRNAMetf, except for slight modifications and replacements. Both species have modifications at three points which do not exist in E. coli tRNAMetf: 2'-O-methylation at G19, N-1-methylation at A59 and 2-thiolation at T55. Moreover U51 in E. coli tRNAMetf is replaced by C51 in both species, so that a G-C pair is formed between this C51 and G65. tRNAMetf2 has a reversed G-C pair at positions 52 and 64 compared with those in tRNAMetf1 and E. coli tRNAMetf. Other regions are mostly the same as those in all prokaryotic initiator tRNAs so far reported. The thermostability of these thermophile initiator tRNAs is discussed in relation to their unique modifications.
