Fig. 4.
Specificity of PSTK. Total calf liver tRNA that had been aminoacylated with all 20 unlabeled amino acids in the presence of rabbit reticulocyte synthetases was fractionated on an RPC-5 column (total of 150 A260 units). The aminoacyl-tRNAs in individual fractions were precipitated, the precipitants were collected and redissolved, and an aliquot was spotted on a nitrocellulose filter and hybridized with a specific Sec tRNA[Ser]Sec probe or added to a reaction containing PSTK and the components for measuring kinase activity. Arbitrary units represent either the 32P determined in the kinase reaction by measuring radioactivity of samples in a scintillation counter (e.g., 10,000 cpm = 10,000 arbitrary units) or the PhosphorImager units measured with 32P-labeled probe in a PhosphorImager (Molecular Dynamics) (e.g., 10,000 PhosphorImager units = 400 arbitrary units).