Uptake of Transfer Ribonucleic Acid by Normal and Leukemic Cells

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Abstract
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 μg/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.