Specific and non-specific mammalian RNA terminal uridylyl transferases

Uridylylation of various types of RNA molecules is a wide-spread phenomenon in molecular biology and is catalyzed by enzymes mediating the transfer of UMP residues to the 3′-ends of preexisting RNA. In most cases, however, the biological significance of these modifications remains elusive. As an exception, the RNA terminal uridylyl transferases (TUTases) of the mRNA editing complex within mitochondria of Trypanosomatidae have been characterized in great detail. Current knowledge on those editing enzymes has been summarized recently by R. Aphasizhev [Cell. Mol. Life Sci. 62 (2005) 2194-203] and, therefore, will not be included here. Rather, this review will focus on cellular non-editing TUTases, characterized by distinct modes of catalytic activity and substrate specificity. Putative biological functions of this rapidly growing number of RNA modifying enzymes are discussed.