Construction of a UGA suppressor tRNA by modification in vitro of yeast tRNACys

In this paper we describe the construction of a yeast tRNACys UGA suppressor. After specific hydrolysis of the parent molecule, the first base of the anticodon GCA was replaced by a uracil. The resulting molecule, harboring a UCA anticodon, was injected into Xenopus laevis oocytes in order to test its biological activities. The level of aminoacylation was similar to that of the parent molecule. Readthrough of the UGA termination codon in beta-globin mRNA, coinjected with the tRNA, indicated suppressor activity; however, tRNACys (anticodon UCA) was a much less efficient suppressor than others tested under the same conditions. We see no post-transcriptional modification of the uracil in the anticodon wobble position after injection into oocytes. This may be related to the low suppressor activity; however, it is also possible that other features of tRNACys structure may be unadapted to efficient UCA anticodon function.