ISOLATION AND CHARACTERIZATION OF REVERTANTS OF THE MAMMALIAN TEMPERATURE SENSITIVE LEUCYL-TRANSFER RNA-SYNTHETASE MUTANT TSHL

Nine spontaneous and 7 ethyl methanesulfonate induced revertants of the Chinese hamster ovary cell line mutant (tsHl), which possesses a temperature sensitive leucyl-tRNA synthetase, were isolated and characterized with respect to growth rate, leucyl-tRNA synthetase activity and thermolability, intracellular Leu pool size and rRNA content. Although most revertants had increased leucyl-tRNA synthetase activity, and all but 1 had increased thermostability, each appeared to be unique. One revertant may be an intergenic suppressor since it appears to contain an elevated level of tsHl-like synthetase. None of the revertants appeared to have increased rRNA and tRNA contents, although many showed leucine pools 2-3 times larger than wild type cells. Since similar increases were observed in tsHl cells they are believed to result from regulation of Leu pool size by the leucyl-tRNA synthetase and are of a magnitude sufficient to significantly affect growth of revertants at 38.5.degree. C.