Purification and Thermal Stability of Several Amino Acid-Specific tRNAs from an Extreme Thermophile, Thermus thermophilus HB8

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Abstract
Three species of methionine tRNAs and phenylalanine, tyrosine, and isoleucine tRNAs were purified from an extreme thermophile, Thermus thermophilus HB8. Formylation studies of the three methionine tRNAs and their codon-specific binding activities to ribosomes showed that two of them (named tRNAMetf1 and tRNAMetf2) were initiator tRNAs and the other (named tRNAMetrn) was a non-initiator. The tRNAs from T. thermophilus all had melting temperatures of up to ten degrees higher than the corresponding species from E. coli. Most of the species also had slightly higher G+C contents than the corresponding species of E. coli, and each of them contained one mol each of the modified nucleosides, O2'-methylguanosine (Gm), 2-thioribothymidine (s2T), and 1-methyladenosine (m1A). Their high melting temperatures could be explained by their high G+C contents and the presence of the modified nucleosides, especially s2T. Comparison of the melting temperatures of T. thermophilus tRNAMetf2 with those of E. coli tRNAMetf and tRNAMetm at different magnesium concentrations showed that magnesium was also a factor in the thermostability of the thermophile tRNA.

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