The CCA end is common to all tRNAs as the universal site for amino acid attachment. It is also conserved in the 3′-terminal tRNA-like structure of viral genomes that can be aminoacylated by an aminoacyl-tRNA synthetase (Florentz & Giegé, 1995). During aminoacylation, the CCA end enters the catalytic center of an aminoacyl-tRNA synthetase and provides the site for chemistry to take place. The CCA end is also widely used in replication of retroviruses, the bacterial single-stranded RNA viruses, and duplex DNA plasmids of fungal mitochondria. During replication, the CCA end interacts with the template-specificity domain of reverse transcriptase or replicase and provides the initiation site for primer binding and extension (Maizels & Weiner, 1994). The importance of the CCA end in translation and in replication suggests that its conformation will play a role in these two fundamental processes.