Uptake of transfer ribonucleic acid by normal and leukemic cells

Uptake of tRNA (Escherichia coli) was demonstrated in the murine leukemia, L1210 and in a human lymphoblast (NC-37) cell lines. In both cell lines, uptake of tRNA was rapid, reaching a maximum within 45 sec, and was linear with concentration up to about 50 mug/ml. This uptake of exogenous tRNA apparently was not due to altered membrane permeability or impaired cell viability, nor to ribonuclease degradation of the macromolecule. Furthermore, about 20% of the tRNA taken up by the cells remains functional and apparently intact. This was demonstrated by: (a) acylation with E. coli aminoacyl-tRNA synthetases; (b) methylation with leukemic cell tRNA-methylases, and (c) demonstrating (14)C-labeled 4S RNA in the cytoplasmic fraction of the leukemic cells after the addition of E. coli [(14)C]tRNA. The results demonstrate that tRNA can enter mammalian cells and suggest that an energy independent, carrier-mediated, mechanism may be operative.