Characterization of Altered Forms of Glycyl Transfer Ribonucleic Acid Synthetase and the Effects of Such Alterations on Aminoacyl Transfer Ribonucleic Acid Synthesis In Vivo
AUTOR(ES)
Folk, William R.
RESUMO
The glycyl transfer ribonucleic acid (tRNA) synthetase (GRS) activities of several Escherichia coli glyS mutants have been partially characterized; the Km for glycine and the apparent Vmax of several of the altered GRS differ significantly from the parental GRS. Paradoxically, some of the altered forms exhibit more activity in vitro than the GRS from a prototrophic strain (GRSL); several parameters of these activities have been studied in an attempt to resolve this problem. The amount of acylated tRNAGly in vivo was examined to assess the GRS activities inside the cells. During exponential growth in media containing glycine, moderate amounts of acylated tRNAGly occur in the glyS mutants; glycine deprivation leads to a dramatic drop in the amount of acylated tRNAGly. An alternative measure of the in vivo activities of the altered enzymes is the efficiency of suppression of the trpA36 locus by su36+; glyS mutants grown with added glycine exhibit one-third to one-fourth the suppression efficiency of the prototrophic glySH parent, presumably because they are less efficient, even in the presence of high levels of glycine, in charging the tRNAGly species which functions as the translational suppressor.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=284987Documentos Relacionados
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