Association of an aminoacyl-tRNA synthetase complex and of phenylalanyl-tRNA synthetase with the cytoskeletal framework fraction from mammalian cells.

The intracellular distribution of several mammalian aminoacyl-tRNA synthetases was investigated by biochemical and immunocytological approaches. The fraction of amino-acyl-tRNA synthetases bound to the detergent-insoluble cytoskeletal framework obtained after extraction of NRK cells by 0.1% Triton X-100 was estimated, by activity measurements, to about 80% for phenylalanyl-tRNA synthetase and 40% for the high-molecular-weight (HMW) complex containing the seven aminoacyl-tRNA synthetases specific for glutamic acid, isoleucine, leucine, methionine, glutamine, lysine, and arginine. This association was shown to be salt-dependent. The subcellular localization of these enzymes was examined using an immunocytological approach. When cultured cells were fixed with paraformaldehyde and then permeabilized with Triton X-100, a fairly uniform cytoplasmic labelling was observed with antibodies directed to the aminoacyl-tRNA synthetase complex or to phenylalanyl-tRNA synthetase. By contrast, when cells were extracted with 0.1% Triton X-100 prior to fixation with paraformaldehyde, the staining patterns obtained with antibodies to aminoacyl-tRNA synthetases were very similar to that obtained with antibodies to rough endoplasmic reticulum, as assessed by single or double indirect immunofluorescence microscopy. These results suggest that free and bound forms of these aminoacyl-tRNA synthetases may coexist within the cell. In addition to cytoplasmic labelling, antibodies directed to phenylalanyl-tRNA synthetase stained the nucleus of rapidly growing cells. The possible significance of this finding is discussed.