Control of arginine biosynthesis in Escherichia coli: role of arginyl-transfer ribonucleic acid synthetase in repression

In vitro transcription of the Escherichia coli K-12 argA, argE, and argCBH operons

Deoxyribonucleic acid isolated from argA and argECBH transducing phages was utilized to study the in vitro synthesis of argA, argE, and argCBH messenger ribonucleic acid. The specific regulation of these operons by the arginine holorepressor was demonstrated, providing evidence that the majority, if not all, of the control of these operons is exercised at the transcriptional level. Data are presented which indicate that the arginine holorepressor functions by binding to the operator region and concomitantly prevents the binding of ribonucleic acid polymerase to the corresponding promoter region.

Regulation of branched-chain amino acid transport in Escherichia coli

The repression and derepression of leucine, isoleucine, and valine transport in Escherichia coli K-12 was examined by using strains auxotrophic for leucine, isoleucine, valine, and methionine. In experiments designed to limit each of these amino acids separately, we demonstrate that leucine limitation alone derepressed the leucine-binding protein, the high-affinity branched-chain amino acid transport system (LIV-I), and the membrane-bound, low-affinity system (LIV-II). This regulation did not seem to involve inactivation of transport components, but represented an increase in the differential rate of synthesis of transport components relative to total cellular proteins. The apparent regulation of transport by isoleucine, valine, and methionine reported elsewhere was shown to require an intact leucine, biosynthetic operon and to result from changes in the level of leucine biosynthetic enzymes. A functional leucyl-transfer ribonucleic acid synthetase was also required for repression of transport. Transport regulation was shown to be essentially independent of ilvA or its gene product, threonine deaminase. The central role of leucine or its derivatives in cellular metabolism in general is discussed.

Genetic mapping of xthA, the structural gene for exonuclease III in Escherichia coli K-12

The genes xthA, pncA, and pabB were ordered relative to others by two- and three-factor transductional crosses with bacteriophage P1. The genes studied span 2 min (2%) of the genetic map of Escherichia coli K-12 in the clockwise sequence pheS-pfkB-xthA-pncA-gap-pabB-fadD. Eleven independently derived xth mutations were examined; all were known to affect exonuclease III and its associated endonuclease II activity, and all were mapped in the xthA region. pncA mutations were found to confer resistance to 6-aminonicotinamide, whereas some pheS mutations are known to specify resistance to p-fluorphenylalanine. xth mutations were readily transferred into other strains by selecting for these co-transducible drug resistance markers.

Dual regulation by arginine of the expression of the Escherichia coli argECBH operon

The correlation between the level of messenger ribonucleic acid (mRNA) specific for the argECBH gene cluster (argECBH mRNA) measured by ribonucleic acid-deoxyribonucleic acid (RNA-DNA) hybridization and the rates of synthesis of N-acetylornithine deacetylase (argE enzyme) and of argininosuccinate lyase (argH enzyme) of Escherichia coli strain K-12 were determined for steady-state growth with and without added L-arginine and during the transition periods between these two states. During the transient period after arginine removal (transient derepression), the synthesis of enzymes argE and argH was initially three to five times greater than the steady-state derepressed rate finally reached 50 min later. The level of argECHB mRNA correlated well both quantitatively and temporally with the rates of enzyme synthesis during this transition. The level of in vivo charged arginyl-transfer RNA (tRNAarg), monitored simultaneously, was initially only 5 to 10% and gradually increased to a final level of 80% after 45 min. During the transient period after arginine addition (transient repression), the rates of synthesis of enzymes argE and argH decreased to almost zero and gradually reached steady-state repressed rates after about 180 min. The argECBH mRNA level remained constant at the steady-state repressed level throughout transient repression, revealing a discontinuity between the level of this mRNA and rates of enzyme synthesis. A similar discrepancy was noted during the transition after ornithine addition. In vivo charged tRNAarg remained constant at 80% during this transition. After removal of arginine, the zero-level transient enzyme synthesis developed after only 7.5 min of arginine deprivation and was maximum after 30 min. The results suggest an accumulation of a molecule regulated by arginine that plays a role in transient repression. Our data indicate that arginyl-tRNA synthetase is not this molecule since its synthesis was unaffected by arginine. The ratios of steady-state argE and argH enzyme synthesis without arginine to that with arginine were 12 and 20, respectively, whereas the similar ratio for argECBH mRNA was 2 to 3. The repressed level of argECBH mRNA was not affected by attempts to repress or derepress the ppc+ gene (carried on the DNA used for hybridization), and the repressed level of argECBH mRNA was lowered about 50% in cells carrying an internal argBH deletion. These data taken together indicate the presence of an excess of untranslated argECBH mRNA during both transient and steady-state repression by arginine. Thus, a second regulatory mechanism, not yet defined, appears to play an important role in arginine regulation of enzyme synthesis.

In vitro synthesis and repression of argininosuccinase in Escherichia coli K12; partial purification of the arginine repressor

Phi80dargECBH DNA has been used to direct cell-free synthesis of argininosuccinase, the argH gene product in Escherichia coli K12. In vitro enzyme synthesis is sensitive to repression by partially purified preparations from an argR+ strain but not by corresponding preparations from an argR- strain. Using DNA-cellulose chromatography, approximately seventyfold purification of repressor has been obtained. The partially purified preparation represses argininosuccinase synthesis but has no effect on beta-galactosidase synthesis.

Accumulation of arginine precursors in Escherichia coli: effects on growth, enzyme repression, and application to the forward selection of arginine auxotrophs

The accumulation or ornithine, citrulline, and possibly acetylornithine by Escherichia coli K-12 arginineless mutants provided with acetylarginine as source of arginine causes severe growth inhibition. This occurs under conditions where comparable derivatives of E. coli W (Bollon and Vogel, 1973) show little or no growth inhibition. The same conditions, which have been reported to cause noncorrelative synthesis of acetylornithinase and argininosuccinase in E. coli W (Bollon and Vogel, 1973), do not alter the correlative pattern of enzyme synthesis observed in E. coli K-12. Moreover, previously reported effects of ornithine and citrulline on repression of the arginine regulon in E. coli W are not observed in the K-12 strains examined. The bearing of these observations on possible differences between the mechanism of enzyme repression operating in the two types of strains cannot yet be fully evaluated; it is, however, clear that considerable care should be exercised before extrapolating the results obtained with one type of strain to the other one. The particularly strong inhibition of acetylarginine utilization exerted by ornithine in E. coli K-12 allows the forward selection of several classes of arginine auxotrophs from strains deficient in carbamoylphosphate biosynthesis and thus capable of ornithine accumulation. Possible applications of this technique to the genetic analysis of the bipolar argECBH operon are discussed.

Control of arginine biosynthesis in Escherichia coli: inhibition of arginyl-transfer ribonucleic acid synthetase activity

In this study, we have extended our earlier observations indicating in vitro inhibition of arginyl-transfer ribonucleic acid synthetase (EC 6.1.13, arginine: soluble ribonucleic acid ligase, adenosine monophosphate) activity by the arginine biosynthetic precursors ornithine, citrulline, and argininosuccinate. Furthermore, we report evidence which suggest that this enzyme activity is inhibited by these arginine precursors in vivo and that this inhibition of activity results in a derepression of arginine biosynthesis.

Control of arginine biosynthesis in Escherichia coli: characterization of arginyl-transfer ribonucleic acid synthetase mutants

The arginyl-transfer ribonucleic acid (Arg-tRNA) synthetase (EC 6.1.1.13, arginine: RNA ligase adenosine monophosphate) mutants, exhibiting nonrepressible synthesis of arginine by exogenous arginine, were employed in studies of several biochemical properties. Two of these mutants possessed Arg-tRNA synthetases with a reduced affinity for arginine, and this enzyme of another mutant had a reduced affinity for arginine-tRNA (tRNA(arg)). The mutant possessing an Arg-tRNA synthetase with an altered K(m) for tRNA(arg) was found to have reduced in vivo aminoacylation of two of the five isoaccepting species of tRNA(arg) and complete absence of aminoacylation of one of the isoaccepting species.