Regulation of the Escherichia coli K-12 uvrB operon

The UV light inducibility of the uvrB operon of Escherichia coli K-12 was previously demonstrated by exploiting a strain in which the gene for the enzyme beta-galactosidase was inserted into the uvrB operon. This insert is now shown to be located within the structural gene for the uvrB enzyme, leaving the regulatory sequences of the operon intact. Analyses to quantitate the induction of this system show that derepression of the operon is first detectable 5 min after UV exposure, with the rate of synthesis increasing to four to six times the uninduced rate during the subsequent 30 min. Induction is unaffected by mutations in other components of nucleotide excision repair. The control of uvrB was found to result from direct repression by the lexA gene product, with the recA gene product playing an indirect role. Nucleotide excision repair thus seems to be part of the SOS response.     

The D-allose operon of Escherichia coli K-12.

Escherichia coli K-12 can utilize D-allose, an all-cis hexose, as a sole carbon source. The operon responsible for D-allose metabolism was localized at 92.8 min of the E. coli linkage map. It consists of six genes, alsRBACEK, which are inducible by D-allose and are under the control of the repressor gene alsR. This operon is also subject to catabolite repression. Three genes, alsB, alsA, and alsC, appear to be necessary for transport of D-allose. D-Allose-binding protein, encoded by alsB, is a periplasmic protein that has an affinity for D-allose, with a Kd of 0.33 microM. As was found for other binding-protein-mediated ABC transporters, the allose transport system includes an ATP-binding component (AlsA) and a transmembrane protein (AlsC). It was found that AlsE (a putative D-allulose-6-phosphate 3-epimerase), but not AlsK (a putative D-allose kinase), is necessary for allose metabolism. During this study, we observed that the D-allose transporter is partially responsible for the low-affinity transport of D-ribose and that strain W3110, an E. coli prototroph, has a defect in the transport of D-allose mediated by the allose permease.     

The cloning of the Escherichia coli K-12 deoxyribonucleoside operon

A 6.1-kb EcoRI DNA fragment containing the four structural genes (deoC, deoA, deoB, deoD) of the deoxyribonucleoside operon has been cloned into the plasmid pMFS53. By use of a unique, asymmetrically positioned HindIII site on the 6.1 kb insert, plasmids containing the deoC,deoA genes (pMFS50) or the deoB,deoD genes (pMFS55) have been constructed. Enzyme assays performed on extracts prepared from clones harboring pMFS53, pMFS50 or pMFS55 revealed that each clone possessed amplified deo enzyme levels and that the spectrum of enzyme amplification corresponded to the genetic composition of the plasmids carried by each clone. A plasmid (pMFS50l) having functional deoA, deoB and deoD genes but devoid of the deo regulatory region and a portion of the deoC structural gene has been isolated following treatment of BamHI cleaved pMFS53 and BAL31 nuclease. Comparison of the deo enzyme levels for clones harboring pMFS53 and pMFS501 suggest that plasmid pMFS53 possesses a functional deo regulatory region in addition to the four structural genes of the operon.     

Complex regulation of the activity of ilv genes in Escherichia coli K-12 cells

The modern data on Escherichia coli K-12 ilv genes expression are reviewed. The problems of regulation of the ilv genes activity and of their possible role in the process of cell adaptation to changeable environment are discussed.     

Operator-constitutive mutants in the threonine operon of Escherichia coli K-12.

Three Escherichia coli K-12 mutant strains resistant to DL-alpha-amino-beta-hydroxyvaleric acid were isolated in which the expression of the thr operon is constitutive. The localization and dominance properties of the mutations involved, called thrO, are those of operator mutations. The gene sequence is OABC as suggested by earlier studies.     

Regulatory mutants of the aroF-tyrA operon of Escherichia coli K-12.

The regulatory region of the aroF-tyrA operon was fused to the chloramphenicol acetyltransferase (cat) gene on a plasmid vector. Expression of the cat gene was subject to repression by tyrR+. This fusion was used to isolate regulatory mutants with increased expression of the cat gene in which repression by tyrR+ was affected. Nucleotide sequencing of these mutants has led to the identification of three sites involved in the repression of aroF by tyrR+. The existence of a functional promoter divergently transcribing from the aroF regulatory region was also demonstrated by using the cat fusion vector. The expression of this promoter is also regulated by tyrR+.     

Secondary promoter of the guanine operon of Escherichia coli K-12.

Evidence of a secondary promoter for the guaA gene within the guaB gene was obtained by using lambdapguaA transducing phage. The technique is generally applicable to distinguish a promoter present within a bacterial deoxyribonucleic acid segment, which has replaced the lambda b2 region of transducing phage, from the phage pI promoter.     

Evidence for the Site of Lambda Insertion in the ilv Gene Cluster of Escherichia coli K-12

The experiments reported herein provide evidence that the secondary site of lambda is in the ilvC instead of the ilvA gene.     

The regulatory region of the divergent argECBH operon in Escherichia coli K-12

The nucleotide sequence of the control region of the divergent argECBH operon has been established in the wild type and in mutants affecting expression of these genes. The argE and argCBH promoters face each other and overlap with an operator region containing two domains which may act as distinct repressor binding sites. A long leader sequence - not involved in attenuation - precedes argCBH. Overlapping of the argCBH promoter and the region involved in ribosome mobilization for argE translation explains the dual effect of some mutations. Mutations causing semi-constitutive expression of argE improve putative promoter sequences within argC. Implications of these results regarding control mechanisms in amino acid biosynthesis and their evolution are discussed.     

Fine structure analysis of the threonine operon in Escherichia coli K-12.

Summary A fine structure analysis of the threonine operon in Escherichia coli K-12 was performed by deletion mapping. Lambda transducing bacteriophages carrying various parts of the threonine operon were isolated from strains in which the lacZ gene was fused to a thr gene. We tested for recombination between deletions of the threonine promotor extending into the threonine operon, carried by the phage, and bacterial thr auxotrophs. The relative order of thrO (operator) mutations was established. We propose that an operator region is located between a promoter region and the structural genes. Mutations leading to the desensitization of the aspartokinase I-homoserine dehydrogenase I towards threonine were localized in two different regions of the thrA gene.