- OXFORD UNIV PRESS
Thermus thermophilus is an extreme-thermophilic eubacterium, which grows at a wide range of temperatures (50-83 degrees C). This thermophile produces various polyamines including long and branched polyamines. In tRNAs from T. thermophilus, three distinct modifications, 2'-O-methylguanosine at position 18 (Gm18), 5-methyl-2-thiouridine at position 54 and N-1-methyladenosine at position 58, are assembled at the elbow region to stabilize the L-shaped tRNA structure. However, the structures of unmodified tRNA precursors are disrupted at high temperatures. We hypothesize that polyamine(s) might have a positive effect on the modification process of unmodified tRNA transcript. We investigated the effects of eight polyamines on Gm18 formation in the yeast tRNA(Phe) transcript by tRNA (Gm18) methyltransferase (TrmH). Higher concentrations of linear polyamines inhibited TrmH activity at 55 degrees C, while optimum concentration increased TrmH activity at 45-75 degrees C. Exceptionally, caldohexamine, a long polyamine, did not show any positive effect on the TrmH activity at 55 degrees C. However, temperature-dependent experiments revealed that 1mM caldohexamine increased TrmH activity at 60-80 degrees C. Furthermore, 0.25mM tetrakis(3-aminopropy)ammonium, a branched polyamine, increased TrmH activity at a broad range of temperatures (40-85 degrees C). Thus, caldohexamine and tetrakis(3-aminopropy)ammonium were found to enhance the TrmH activity at high temperatures.
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