Yeast tRNA (guanosine(18)-2'-O)-methyltransferase TRM3 catalyzes the formation of 2'-O-methylguanosine at position 18 (Gm18) in various tRNAs. TRM3 is similar to C-terminal domain of TAR (HIV-1) RNA binding protein 1 (TARBP1), a protein binding to TAR, which functions as a RNA regulatory signal by forming a stable stem-loop structure to which transactivator protein Tat binds. The role of TARBP1 is believed to be to disengage RNA polymerase II from TAR during transcriptional elongation. TRM3 and the C-terminal methyltransferase domain of TARBP1 are members of the SPOUT methyltransferase superfamily.
Jiyao W et al.(2023). "The conserved domain database in 2023.",