Irreversible inactivation at high temperature of temperature-sensitive mutant tRNA Tyr in vivo

INTRACELLULAR RNA species may be classified into two groups, one with rapid turnover such as messenger RNA (mRNA) and the other which is fairly stable such as ribosomal RNA (rRNA) or transfer RNA (tRNA). The latter group presumably maintains a tertiary structure more resistant to enzymatic digestion. In the case of tRNA especially, the RNA molecules are not complexed with protein as is rRNA, so it is probable that the tertiary structure of the tRNA molecule itself is responsible for its stability in the cell. To check this, in vivo measurement of the functional activity of tRNA which had undergone transient and partial unfolding was necessary. If partially unfolded tRNA could be distinguished from normal tRNA and attacked by hydrolytic enzymes in vivo, activity of this tRNA would not be expressed even after transient unfolding had stopped. For this, a tRNA species was needed whose conformation loosened under certain conditions in vivo.