A role for aminoacyl-tRNA synthetases in the regulation of amino acid transport in mammalian cell lines.

The regulation of neutral amino acid transport was examined utilizing two temperature-sensitive aminoacyl-tRNA synthetase mutants, by comparison of their transport activities at permissive and marginally permissive temperatures. When the temperature-sensitive leucyl-tRNA -synthetase mutant tsH1 was shifted from a normal growth temperature of 34 degrees to a marginally permissive temperature for growth of 38%, a significant enhancement in the initial rate of uptake of leucine and other L system amino acids was observed when compared with that of the parental cells (CHO-S). In contrast, the uptake of A system-specific amino acids (alanine, glycine, alpha-aminoisobutyric acid) showed no significant differences relative to the parent strain. In a similar manner, a temperature-sensitive asparaginyl-tRNA synthetase mutant RJK-4 exhibited a significant enhancement of the transport activity of A system amino acids relative to its parental strain RJK-0 when the growth temperature was shifted from 33 degrees to 39.5 degrees. Preliminary kinetic data suggest that the Vmax for transport is increased when the mutants are grown under conditions of amino acid limitation. These experiments suggest that the aminoacyl-tRNA synthetase or a related product may function in the regulation of neutral amino acid transport in Chinese hamster cells.