Yeast seryl-tRNA synthetase expressed in Escherichia coli recognizes bacterial serine-specific tRNAs in vivo

Abstract

The Saccharomyces cerevisiae serS gene which encodes seryl-tRNA synthetase (SerRS) was expressed in Escherichia coli from the promoter and the ribosome binding sequences contained in its own 5'-flanking region. The low level of yeast SerRS in the prokaryotic host was sufficient to permit in vivo complementation of two temperature-sensitive E. coli serS mutants at the nonpermissive temperature. Thus, yeast SerRS can aminoacylate E. coli tRNA(Ser) species in vivo. Yeast SerRS, isolated from an overexpressing E. coli strain by a rapid two-step purification on FPLC, aminoacylated E. coli tRNA with serine much more poorly (relative kcat/Km = 2 x 10(-4)) than its homologous tRNAs. DL-Serine hydroxamate, an inhibitor of E. coli SerRS, inhibits yeast SerRS in vivo and in vitro with an inhibition constant (Ki) of 2.7 mM, a value 90-fold higher than that for E. coli SerRS.