Repression of Enzymes of Arginine Biosynthesis by l -Canavanine in Arginyl-Transfer Ribonucleic Acid Synthetase Mutants of Escherichia coli

Abstract

We show that the arginine analogue, l -canavanine, repressed the accumulation of translatable messenger ribonucleic acid (RNA) for three arginine biosynthetic enzymes in Escherichia coli . The method used to determine the level of translatable messenger RNA depended upon measurement of a burst of enzyme synthesis as described previously. E. coli strains with defective arginyltransfer ribonucleic acid (tRNA) synthetase ( argS mutants) were insensitive to canavanine repression. When deprived of leucine, a leu argS strain regained normal sensitivity to canavanine repression. The level of in vivo canavanyl-tRNA arg was determined for a normal strain and an argS mutant. After 20 min of growth with canavanine only 9% of tRNA arg from the argS strain was protected from periodate oxidation, while 42% of the tRNA arg from an argS + strain was charged. When deprived of leucine, leu argS or leu argS + strains grown with canavanine contained more than 60% charged tRNA arg . Reverse phase column chromatography of periodate-oxidized tRNA from canavanine-grown argS and argS + strains showed no preferential charging of any isoaccepting species of tRNA arg . Therefore, we failed to detect a specific arginyl-tRNA species that might be involved in repression by canavanine. However, the data suggest that canavanine repression of the arginine pathway occurs only when high levels of canavanyl-tRNA are present, and thus support the notion that arginyl-tRNA synthetase plays a role in generating a repression signal.