TRAM, a predicted RNA-binding domain, common to tRNA uracil methylation and adenine thiolation enzymes

A previously undetected conserved domain is identified in two distinct classes of tRNA-modifying enzymes, namely uridine methylases of the TRM2 family and enzymes of the MiaB family that are involved in 2-methylthioadenine formation. This domain, for which the acronym TRAM is proposed after TRM2 and MiaB, is predicted to bind tRNA and deliver the RNA-modifying enzymatic domains to their targets. In addition to the two families of RNA-modifying enzymes, the TRAM domain is present in several other proteins associated with the translation machinery and in a family of small, uncharacterized archaeal proteins that are predicted to have a role in the regulation of tRNA modification or translation. Secondary structure prediction indicates that the TRAM domain adopts a simple beta-barrel fold. In addition, sequence analysis of the MiaB family enzymes showed that they share the predicted catalytic site with biotin and lipoate synthases and probably employ the same mechanism for sulfur insertion into their respective substrate.