Improved solid-phase DNA probe method for tRNA purification: large-scale preparation and alteration of DNA fixation.

The solid-phase DNA probe method, in which a target transfer RNA (tRNA) is hybridized with a complementary DNA oligomer, is generally used for tRNA purification. However, purification of tRNAs from thermophiles by this method is not easy because of their high melting temperatures. To overcome this problem, the use of tetraalkylammonium salts was previously reported [Yokogawa, T., Kitamura, Y., Nakamura, D., Ohno, S., and Nishikawa, K. (2010) Optimization of the hybridization-based method for purification of thermostable tRNAs in the presence of tetraalkylammonium salts. Nucleic Acids Res. 38, e89]. In this study, we initially devised a large-scale purification system using tetraalkylammonium salts. The yield of tRNA was increased more than 10-fold and the manual steps were decreased as compared with the previous procedure. However, deterioration of column was very rapid owing to shedding of the biotinylated DNA probe. We therefore devised a method of covalent DNA fixation, in which a 5'-aminohexyl (dT)8 oligomer was fixed onto the N-hydroxysuccinimide-activated agarose, and then a DNA oligomer containing the tRNA and repeated A8 sequences was annealed. The probe sequence for tRNA purification was synthesized in column with Klenow enzyme. This DNA fixation method enabled us to use the column repeatedly and to wash the column with warmed buffers. Thus, this DNA fixation method is economical as compared with the previous method using the biotinylated DNA probe.