A Eubacterial Origin for the Human tRNA Nucleotidyltransferase?

in E. coli, because all of its tRNA genes encode the CCA-terminus. However, reduced growth rates and increased amounts of 3’-truncated tRNAs are observed when the corresponding gene cca is inactivated (Deutscher and Hilderman, 1974; Deutscher et al., 1977; Zhu and Deutscher, 1987). In contrast, the enzyme is essential for eukaryotes, archaea, and many other eubacteria, where only very few tRNA genes encode the CCA-terminus (Deutscher, 1990). In budding yeast the essential nature of the cca gene has been shown using a temperature-sensitive tRNA nucleotidyltransferase mutant, which showed growth arrest and an enrichment of 3’-truncated tRNAs upon shifting the cells to the non-permissive tem-perature (Aebi et al., 1990). The CCA-adding enzyme belongs to an ancient nu