Accelerated publication - Active aminoacyl-tRNA synthetases are present innuclei as a high molecular weight multienzyme complex

Recent studies suggest that aminoacylation of tRNA may play an important ro le in the transport of these molecules from the nucleus to the cytoplasm. H owever, there is almost no information regarding the status of active amino acyl-tRNA synthetases within the nuclei of eukaryotic cells. Here we show t hat at least 13 active aminoacyl-tRNA synthetases are present in purified n uclei of both Chinese hamster ovary and rabbit kidney cells, although their steady-state levels represent only a small percentage of those found in th e cytoplasm. Most interestingly, all the nuclear aminoacyl-tRNA synthetases examined can be isolated as part of a multienzyme complex that is more sta ble, and consequently larger, than the comparable complex isolated from the cytoplasm. These data directly demonstrate the presence of active aminoacy l-tRNA synthetases in mammalian cell nuclei. Moreover, their unexpected str uctural organization raises important questions about the functional signif icance of these multienzyme complexes and whether they might play a more di rect role in nuclear to cytoplasmic transport of tRNAs.