Separation and comparison of 2-thioribothymidine-containing transfer ribonucleic acids and the ribothymidine-containing counterpart from cells of Thermus thermophilus HB 8

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Abstract
For the extreme thermophile T. thermophilus HB 8, a positive correlation was observed among the growth temperatures of the cells, the melting temperature, and the 2-thioribothymidine (s2T) content of tRNA extracted from cells grown at various temperatures. On the basis of these observations, studies were carried out from which the following results were obtained. Both RNase T1 and U2 digestions of tRNA gave only 4 fragments containing s2T or T: s2T.psi.CGp, s2T.psi.CAp, T.psi.CGp and T.psi.CAp. For the different growth temperatures, the ratio of the content of s2T.psi.CGp plus s2T.psi.CAp to that of T.psi.CGp plus T.psi.CAp was almost the same as that of the s2Tp to Tp content reported previously. The midpoint of the s2T-specific circular dichroism spectral change induced by heat was constant for all tRNA species extracted from cells grown at various temperatures, suggesting that the s2T-containing tRNA species melt at about the same temperature, which is independent of the growth temperature of cells. s2T-containing tRNA was separated from the T-containing counterpart quantitatively by a specific modification of s2T with bromoaceto-2,4-dinitroanilide followed by BD-cellulose column chromatography. The molar ratio of the s2T- and T-containing tRNA species was also similar to that of s2Tp to Tp as mentioned above. T. thermophilus cells apparently have both s2T- and T-containing tRNA species, and their relative contents may be controlled by the growth temperature. This phenomenon may be necessary to enable the thermophile to adapt to higher temperatures.

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