Aminoacyl-tRNA synmthstase complexes : variability in mutants and in 10X LIV medium
Condon, Thomas P.
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The aminoacyl-tRNA synthetase (aaRS) complexes from three Chinese Hamster Ovary (CHO) cell lines were characterized by sucrose gradient sedimentation analysis. The mutant Gin-2 contains an altered glutaminyl-tRNA synthetase C GlnRS ) which has lost the low molecular weight form. The Lys-101 mutant exhibited an almost complete loss of lysyl-tRNA synthetase ( LysRS ) activity. All other aaRS activities were normal in the mutants Gin-2 and Lys-101.‘ The mutant, His-1, contained a reduced level of histidyl-tRNA synthetase (HisRS) activity, but also changes in several other aaRS activities. The CHO cell, temperature sensitive leucyl-tRNA synthetase (LeuRS) mutant tsHl, was grown in alpha minimal essential medium ( MEM) supplemented with tenfold concentrations of leucine (Leu), isoleucine (lie) and valine (Val or all together 10X LIV). The temperature sensitive phenotype is reversed when grown in the 10X LIV medium. It was found here that a partial restoration of the high molecular weight LeuRS complexes had occurred in the 10X LIV medium. The ability of tsHl to grow at the nonpermissive temperature appears to be due to the presence of the.high molecular weight complexes. The mechanism of LeuRS complex restoration remains to be elucidated.