Aquifex aeolicus is a hyper-thermophilic eubacterium, which probably diverged at the earliest period from the other bacteria on the evolution of life. Therefore, analyses of RNA modification enzymes of this bacterium may supply important information in relation to the establishment of the early protein synthesis. In the previous meeting, we have reported that Aquifex aeolicus trm1 gene product possesses a tRNA (m2(2)G26) methyltransferase activity. This enzyme catalyzes the methyl-transfer from S-adenosyl-L-methionine to the semi-conserved residue, G26, via the intermediate modified base, m2G26. In this meeting, we report the A. aeolicus Trm1 large scale expression system in E. coli and the substrate RNA recognition mechanism of the enzyme.