Effect of arginine on the stability and size of argECBH messenger ribonucleic acid in Escherichia coli

Metabolic engineering of Escherichia coli for efficient production of l-arginine

As a semi-essential amino acid, l-arginine (l-Arg) plays an important role in food, health care, and medical treatment. At present, the main method of producing l-Arg is the use of microbial fermentation. Therefore, the selection and breeding of high-efficiency microbial strains is the top priority. To continuously improve the l-Arg production performance of the strains, a series of metabolic engineering strategies have been tried to transform the strains. The production of l-Arg by metabolically engineered Corynebacterium glutamicum (C. glutamicum) reached a relatively high level. Escherichia coli (E. coli), as a strain with great potential for l-Arg production, also has a large number of research strategies aimed at screening effective E. coli for producing l-Arg. E. coli also has a number of advantages over C. glutamicum in producing l-Arg. Therefore, it is of great significance to screen out excellent and stable E. coli to produce l-Arg. Here, based on recent research results, we review the metabolic pathways of l-Arg production in E. coli, the research progress of l-Arg production in E. coli, and various regulatory strategies implemented in E. coli.

Biosynthesis of Arginine and Polyamines

Early investigations on arginine biosynthesis brought to light basic features of metabolic regulation. The most significant advances of the last 10 to 15 years concern the arginine repressor, its structure and mode of action in both E. coli and Salmonella typhimurium, the sequence analysis of all arg structural genes in E. coli and Salmonella typhimurium, the resulting evolutionary inferences, and the dual regulation of the carAB operon. This review provides an overall picture of the pathways, their interconnections, the regulatory circuits involved, and the resulting interferences between arginine and polyamine biosynthesis. Carbamoylphosphate is a precursor common to arginine and the pyrimidines. In both Escherichia coli and Salmonella enterica serovar Typhimurium, it is produced by a single synthetase, carbamoylphosphate synthetase (CPSase), with glutamine as the physiological amino group donor. This situation contrasts with the existence of separate enzymes specific for arginine and pyrimidine biosynthesis in Bacillus subtilis and fungi. Polyamine biosynthesis has been particularly well studied in E. coli, and the cognate genes have been identified in the Salmonella genome as well, including those involved in transport functions. The review summarizes what is known about the enzymes involved in the arginine pathway of E. coli and S. enterica serovar Typhimurium; homologous genes were identified in both organisms, except argF (encoding a supplementary OTCase), which is lacking in Salmonella. Several examples of putative enzyme recruitment (homologous enzymes performing analogous functions) are also presented.

Expression of arg genes of Escherichia coli during arginine limitation dependent upon stringent control of translation

The transcription and translation of operons for arginine biosynthetic enzymes after arginine removal (arginine down shift) were studied in relA and relA+ strains of Escherichia coli. After arginine down shift, derepression of synthesis of the arginine biosynthetic enzymes ornithine carbamoyltransferase (argF) and argininosuccinate lyase (argH) began at about 15 min in relA+ cells but was delayed in relA cells for more than 2 h. However, both relA+ and relA cells accumulated high levels of argCBH mRNA, as shown by dot blot hybridization, after arginine down shift. After 15 min of arginine limitation, the proportion of ribosome-bound argCBH mRNA was equivalent in both relA+ and relA cells. During the 15 min after the arginine down shift, relA+ cells produced a significant burst of argF and argH enzyme synthesis when arginine was added back to the culture, whereas relA cells did not produce this burst of enzyme synthesis. The relA cells regained the ability to produce a burst of argF and argH enzyme synthesis when alpha-methylglucose-induced glucose starvation was combined with arginine limitation. Significant guanosine 5'-diphosphate 3'-diphosphate accumulated in relA cells under this condition. Our results support the view that during periods of severe amino acid limitation guanosine 5'-diphosphate 3'-diphosphate acts in some way to ensure the translation of argCBH mRNA.

Regulation and coupling of argECBH mRNA and enzyme synthesis in cell extracts of Escherichia coli

Cell extracts from Escherichia coli were used to study both transcription and coupled translation of the argECBH gene cluster. Argininosuccinase (the argH enzyme) and N-acetylornithinase (the argE enzyme) were synthesized for 90 to 120 min, and hybridizable argECBH mRNA was synthesized for 60 min after the addition of a lambda or phi 80 dargECBH DNA template. L-Arginine (2.5 mM) repressed synthesis by argR+ extracts of argECBH mRNA 2-, to 3-fold, argE enzyme 5- to 8-fold, and argH enzyme 20- to 60-fold. Repression was specific for L-arginine, and argR extracts were insensitive to added L-arginine. The argECBH mRNA made under conditions of restricted protein synthesis had reduced ability to function in the formation of the argE and argH enzymes and was found to be predominantly 6 to 8S in sucrose density gradients. When protein synthesis was allowed, the mRNA formed was functional, and large amounts of 14 to 23S argECBH mRNA appeared on sucrose gradients. An S-100 supernatant freed of ribosomes was capable of producing hybridizable arg mRNA, but significant functional message was only produced when ribosomes were present. When purified RNA polymerase was used, the formation of short 6 to 8S argECBH mRNA was dependent upon added rho protein. The data suggest that rho-dependent sites in the argECBH operon allow early termination of mRNA synthesis when transcription is not coupled to active enzyme synthesis.

Positive control of expression of the argECBH gene cluster in vitro by guanosine 5'-diphosphate 3'-diphosphate

By using a cell-free system derived from Escherichia coli, it was found that guanosine 5'-diphosphate 3'-diphosphate (ppGpp) was a positive effector for expression of both wings of bidirectionally transcribed argECBH gene cluster. A 7- to 20-fold increase in the synthesis of both argininosuccinase (the argH enzyme) and N-acetylornithinase (the argE enzyme) resulted with added ppGpp (0.2 mM optimum). Synthesis of hybridizable argECBH mRNA was enhanced only 30 to 100% by added ppGpp. Of the various guanosine nucleotides tested, only pppGpp mimicked ppGpp. Added ppGpp had no important effect upon (i) measurable argE or argH enzyme activity, (ii) total protein synthesis in the cell-free system, or (iii) the rate of decay of hybridizable argECBH mRNA. With extracts of an argR+ strain, added ppGpp had no effect on the repression of enzyme or mRNA synthesis by L-arginine. By using a two-stage system in which the bulk of argECBH mRNA was synthesized while protein synthesis was delayed, we showed that ppGpp acted at some point during transcription.

The determination by radiochemical assay of argininosuccinase produced in an Escherichia coli system in vitro

A highly sensitive radiochemical assay used to measure the synthesis and regulation of the product of the argH gene, argininosuccinase, in an Escherichia coli system in vitro is described. With L-[guanidino-14C]argininosuccinic acid as a substrate, and in the presence of excess arginase and urease, 14CO2 is collected in a simply designed micro-vessel. With this method less than 1 nmol of product can be measured in the presence of various concentrations of L-arginine.

Transcription of Regions within the divergent argECBH operon of Escherichia coli: evidence for lack of an attenuation mechanism

Using in vitro and in vivo assays, we could detect no early termination of DNA transcription in the proximal part of the argCBH arm of the argECBH divergent operon. The discrepancy noted previously between the respective amplitudes of variation of messenger and enzyme synthesis must therefore be attributed to other causes than a difference in efficiency between attenuation and repression.

Cloning and endonuclease restriction analysis of argF and of the control region of the argECBH bipolar operon in Escherichia coli

A 1.8 kb DNA fragment, liberated by endonuclease HindIII, contains the control region of the argECBH bipolar operon near one end and the weak secondary promoter of argH at the other extremity; it has been cloned in plasmid pBR322. The same plasmid vector has been used to clone the argF gene liberated from the chromosome by endonuclease BamHI. Restriction patterns for the two hybrid plasmids have been determined, using enzymes AluI, BglI, EcoRI, HaeIII, HincII, HindIII, HpaI and II, PstI and SalI. Two AluI sites situated on either side of and close to a HincII target delineate two short fragments covering the whole of the argECBH control region. The argF control elements are located in a region accessible to further dissection by BamHI, EcoRI, PstI and HindIII. Carriers of the argF plasmid produce extremely high amounts of ornithine carbamoyltransferase, a feature useful for purification of this enzyme.

Evidence for translational repression of arginine biosynthetic enzymes in Escherichia coli: altered regulation in a streptomycin-resistant mutant

The formation and repressibility of the arginine biosyntietic enzymes acetylornithine delta-aminotransferase (EC 2.6.1.11), acetylornithine deacetylase (EC 3.5.1.16), ornithine carbamoyltransferase (EC 2.1.3.3), and argininosuccinate lyase (EC 4.3.2.1) were studied in an Escherichia coli W derivative (strain 250-10) that carries (a) a mutant allele of the argR regulatory gene causing a diminished repression-derepression range and (b) a streptomycin resistance mutation. In comparison with the streptomycin-sensitive parent 250, all four enzymes (a) are formed as smaller proportions of the total protein (overall range, 12% to 71%), whether the conditions are repressive (arginine excess) or derepressive (arginine restriction), and (b) show increased repressibility ratios, the carbamoyltransferase giving the largest increase (from 5.7 to 25.0). These effects appear to depend on the concurrent expression of the regulatory-gene and streptomycin resistance mutations, as indicated by analogous experiments with canavanine-resistant mutants of 250-10 that have partial argR- character. The results provide evidence for translational repression in the arginine system, and are interpreted in terms of a functional interaction of a mutant arginine repressor with a mutant S12 ribosomal protein. The locale of translational repression may be near the site of S12, and this mode of regulation may involve initiational selectivity of groupwise recognizable arginine messenger RNA's.

Studies on the control region of the bipolar argECBH operon of Escherichia coli. I. Effect of regulatory mutations and IS2 insertions

Several mutations affecting the control or the potential of gene expression in the argECBH bipolar operon have been characterized by enzyme assays, genetic mapping, dominance tests and pulse labelled RNA determinations. None of the mutations involves DNA rearrangements detectable by heteroduplex analysis (Charlier et al., 1978). Partially constitutive transcription of both argE and argCBH has been observed in mutant L10 while constitutive argE transcription and normal argCBH control characterize mutants L9, LL13 and LL2. The control region thus appears to contain two overlapping operators, as suggested previously (Elseviers et al., 1972). Two mutants (L2, LL1) and strain 6-8 from Bretscher and Baumberg (1976) display an increase in acetylornithinase specific activity (argE product) without concommittant increased argE transcription. In addition, they exhibit a decreased argCBH transcription. It is suggested that in these organisms, argE translation and argCBH transcription may be affected by the same genetic event; this explanation is compatible with present working hypothesis for the structure of the control region. An interpretation in terms of messenger attenuation also appears possible. From the properties of two strains harbouring an IS2 insertion in the control region (Charlier et al., 1978) the following conclusion may be drawn: 1. When inserted in orientation I close to the proximal end of a silent gene IS2 appears to promote a low but detectable transcription readthrough into that gene. 2. Insertion of an IS2 element in orientation II close to a neighbouring gene is not a sufficient condition to express that gene at a high rate. The properties of the two insertions appear compatible with the structure proposed for the control region.

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.

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.