Characterization of transfer RNA from liver of the developing amphibian, Rana catesbeiana

The measurement of the production of tRNAMet1 in the Friend erythroleukemia cell

We have used the gene for tRNAMet1 as a hybridization probe to measure the production of tRNAMet1 in the Friend erythroleukemia cell. In this cell, the relative concentration of tRNAMet1 (i.e., the percentage of total steady-state tRNA representing tRNAMet1) is 1.60 +/- 0.18. To study the relative synthesis of tRNAMet1, cells were labeled in vivo with [3H]uridine for periods ranging from 4 to 24 h, and the tRNA was isolated. The fraction of newly-synthesized tRNA representing tRNAMet1 (1.72% +/- 0.11) does not change when different in vivo labeling times are used. This value is similar to the relative concentration of tRNAMet1 in the older steady-state tRNA (1.61% +/- 0.18). The similar relative synthesis values using different labeling times, plus evidence presented that the total tRNA population decays homogeneously (t 1/2 = 110 h) indicate that tRNAMet1 has a cytoplasmic stability similar to the general tRNA population, and that its concentration relative to the tRNA population is established within the nucleus or soon after exiting the nucleus. Measurements of the synthesis of tRNAMet1 in isolated nuclei, relative to the synthesis of total RNA polymerase III transcripts, showed that this relative synthesis (0.291% +/- 0.017) is only 17% of the relative concentration of tRNAMet1 in the cytoplasm, which may reflect the presence of sequences other than tRNA in total nuclear polymerase III transcripts.

Transfer ribonucleic acid populations in concanavalin-A-stimulated bovine lymphocytes

Transfer RNA isolated from lymphocytes stimulated by concanavalin A and that from resting cells were compared with respect to amino-acid acceptance, integrity of the CCA-terminus, extent of modification and isoacceptor distribution. Following growth stimulation the overall amino-acid acceptance of the tRNA is elevated, in particular the relative acceptor activities for threonine and arginine are increased. The reduced acceptor activity of the tRNA from the quiescent cells is not due to a preferential degradation of the CCA-end, since it persists even in the presence of ATP(CTP):tRNA nucleotidyltransferase. We therefore conclude that this reduced activity is caused by structural differences of the tRNAs. The content of modified nucleotides in newly synthesized tRNA from lymphocytes cultured in the presence and absence of concanavalin A was determined. tRNA from resting cells was found to be undermodified with respect to pseudouridine and dihydrouridine. Upon monitoring the tRNA isoacceptor distribution by affinity chromatography on immobilized elongation factor Tu and subsequent two-dimensional gel electrophoresis, a preferential synthesis of particular lysine- and threonine-accepting tRNAs was observed upon mitogenic stimulation. Evidently, a specific tRNA population is needed by the proliferating cells. These results are discussed in view of the hypothesis that the commitment of lymphocytes to proliferation is at least in part under translational control.