The phi80 lambdadilv phage and its use to detect messenger RNA related to isoleucine-valine metabolism

Genetical and structural analysis of a group of lambda ilv and lambda rho transducing phages

Eight lambda ilv C transducing phages generated from E. coli K12 secondary site lysogens have been analysed genetically and physically. Two of them carry, in addition, the rho gene and its promotor region, but not the cya gene. The ilv O 603 mutation has been located between ilv G and ilv E. Electrophoretic analysis of the proteins synthesized by these phages in a system of UV irradiated cells allowed us to assign molecular weights of 55000 and 66000 daltons to the ilv C and the ilv D gene products, respectively, and to show that an ilv G-encoded polypeptide of 60000 daltons is made from an ilv O- but not from an ilv O+ phage. The expression of the ilv G gene is discussed in the light of the recent finding of a promoter-attenuator region lying upstream to ilv G. Finally, we have found that one of the lambda ilv phages does not have the classical structure of a transducing phage.

Regulation of ilvEDA expression occurs upstream of ilvG in Escherichia coli: additional evidence for an ilvGEDA operon

A low-copy-number plasmid was prepared that contained the entire ilv gene cluster of Escherichia coli. The introduction of an ilvO mutation allowed the ilvG gene of the plasmid to be expressed and imparted valine resistance to strains carrying it. Insertion of Tn10 into the ilvG gene of the plasmid resulted in a strong polar effect on ilv genes E, D, and A. Replacement of a region of ilv deoxyribonucleic acid between two KpnI sites on the high-copy-number plasmid carrying the entire ilv gene cluster with a KpnI fragment carrying an ilv-lac fusion but not extending into the ilv-specific control region resulted in a plasmid expressing the lacZ gene under ilv control when the fusion had been inserted in its normal orientation but not when it had been inserted in the opposite orientation. These experiments indicate that ilv-specific control over ilvE, ilvD, and ilvA expression is dependent on these genes being continguous with deoxyribonucleic acid that lies upstream of ilvG. The results also add further support to the concept of an ilvGEDA operon in E. coli.

Physical location of the ilvO determinant in Escherichia coli K-12 deoxyribonucleic acid

A plasmid carrying the 4,6-kilobase (kb) HindIII-derived fragment from an ilvO mutant derivative of lambda h80dilv imparted a valine-resistant phenotype on strains it carried. This fragment carries a small amount of the promoter-proximal end of ilvE, the ilvO determinant, and apparently the entire ilvG gene, which specifies the valine-insensitive acetohydroxy acid synthase. Comparable deoxyribonucleic acid (DNA) from the original lambda h80dilv did not carry the valine resistance marker. The valine-resistant phenotype was always correlated with the formation of the resistant enzymes. The ilvO determinant was shown to be carried within an approximately 600-based-pair region lying between the SalI and KpnI sites on the HindIII fragment and perhaps within the ilvG gene itself. Ribonucleic acid that hybridizes with the DNA corresponding to the ilvG gene is formed in wild-type K-12 cells. This fact, coupled with the fact that ilvG is transcribed from the same DNA strand as the ilvE, D, and A genes, led to the idea that transcription is normally initiated upstream from ilvG in both wild-type and ilvO strains. In wild-type strains either the formation or the translation of the transcript would be terminated with the ilvG gene, thus preventing expression of that gene.

Physical characterization of ilv-lac fusions

Electron microscopic heteroduplex analysis and comparative restriction digests have been used to characterize lambda p123(209), the complementary pair of phages used in the Casadaban technique of gene fusion. Derivatives of lambda 1(209) constructed to carry fusions of the lac genes to the control regions of the ilvC and ilvEDA operons were also analyzed. These physical maps have provided confirmation of the genetic models for these constructions and physical specifications important in interpreting the behavior of these ilv-lac fusions.

Correlation between the serine sensitivity and the derepressibility of the ilv genes in Escherichia coli relA- mutants

Upon addition of excess one carbon metabolites (including serine)bacteria stop growing because of isoleucine starvation. After such treatment stringent bacteria rapidly resume normal growth whereas relaxed mutants remain unable for some time to grow. We show here that this is due to a lack of derepressibility of ilv genes after the starvation period. Results are also presented which show that RNA polymerase structural mutants may be selected among the clones resistant to a mixture of serine, methionine and glycine, in relA- strains. Finally circumstancial evidence suggests that the one carbon metabolism may be involved in a process controlling isoleucine metabolism.

Dual autogenous regulatory role of threonine deaminase in Escherichia coli K-12

We describe the regulatory properties of two strains carrying either the ilvA624 or the ilvA625 mutations, located in the structural gene for threonine deaminase. Crude extracts of both these strains possess a threonine deaminase activity migrating on polyacrylamide gels, differently from the wild type enzyme. Growth studies demonstrate that these mutations do not cause a limitation of isoleucine biosynthesis, suggesting normal catalytic activity of deaminase. A regulatory consequence of the ilvA624 allele is a derepression of the isoleucine-valine biosynthetic enzymes, which is recessive to an ilvA+ allele. The ilvA625 mutation causes a derepression which is dominant in an ilvA625/ILVA+ diploid. We interpret these data assuming that threonine deaminase, previously shown to be an autogenous regulator of the ilv genes, lacks a repressor function in the ilvA624 mutant, while in the ilvA625 mutant it is a better activator than wild type threonine deaminase. The data are discussed in terms of a model requiring that threonine deaminase, or a precursor of it, is in equilibrium between two forms, one being an activator of gene expression and the other being a repressor.

Characterization of fusions between the lac operon and the ilv gene cluster in Escherichia coli: ilvC-lac fusions

By means of the general procedure of Casadaban (J. Mol. Biol. 104: 541-556, 1976), the lac genes carried on a lambda-Mu-1 hybrid phage were inserted into a temperature-inducible Mu-1 prophage that had earlier been inserted into a site near the beginning of the ilvC gene of Escherichia coli strain K-12. Selection of temperature-resistant derivatives of the lysogen resulted in a fusion of the lac genes to a region of deoxyribonucleic acid that is transcribed under the control of the ilvC regulatory elements. A strain bearing the fusion was shown to be inducible for beta-galactosidase by acetohydroxybutyrate, a natural inducer of acetohydroxy acid isomeroreductase. Induction of the lysogen by mitomycin C led to the isolation of a plaque-forming lambda derivative carrying this ilvC-lac fusion.

Growth inhibition of Escherichia coli K-12 by L-valine: a consequence of a regulatory pattern

We studied the production of the ilvG gene product, the valine resistant acetolactate synthase isoenzyme II, in an ilvO+ G+ ilvB ilvHI derivative of Escherichia coli K-12. This strain contains mutations in the structural genes for the valine sensitive acetolactate synthase isoenzymes I and III. We find that the ilvG gene is not expressed in this strain when gworn with either isoleucine and valine or with isoleucine, leucine and valine, or when limited for either isoleucine or valine. Since we previously found that the ilvG gene is expressed in an ilvO603 containing strain (Favre et al., 1976), we presume that the mechanism by which E. coli K-12 regulates the ilv gene cluster is responsible for the lack of ilvG expression in the ilvO+ strain. The valine sensitivity of E. Coli K-12 is a consequence of this regulatory pattern.

Detection of messenger RNA from the isoleucine--valine operons of Salmonella typhimurium by heterologous DNA-RNA hybridization: involvement of transfer RNA in transcriptional repression

A hybridization assay using Escherichia coli K-12 DNA isolated from the specialized transducing bacteriophage gammaCI857St68h80 dilv was used to examine the rate of synthesis of the messenger RNA's (mRNA) derived from the isoleucine-valine (ilv) gene cluster of Salmonella typhimurium. In all cases examined, changes in ilv enzyme levels could be correlated with changes in the rate of synthesis of ilv mRNA. Several well characterized regulatory mutants of S. typhimurium had rates of synthesis of ilv mRNA 3 to 8-fold higher than the repressed wild-type strain. The increased rates of ilv mRNA synthesis found in a hisT strain as well as in isoleucyl-and leucyl-tRNA SYNTHETASE MUTANTS, STRONGLY SUGGESTS A ROLE FOR BRANCHED-CHAIN AMINOACYL-TRNA's in transcriptional control.

Polarity and the regulation of the ilv gene cluster in Escherichia coli strain K-12

A series of Mu-1 induced isoleucine and valine auxotrophs derived from the wild type K-12 strain of Escherichia coli and from a valine resistant (ilvO-) mutant were examined. It was concluded that the genes ilvE, ilvD and ilvA constitute a single operon and are transcribed from E to A. Furthermore, the ilvG gene, expressed only in ilvO- strains, does not lie between ilvE and ilvD as previously assumed. A mutation in rho was examined for its effect on the ilvEDA operon. One effect of the rho- mutation was a mimicking of an isoleucine limitation signal. A model for the regulation of the ilvEDA operon is discussed. The model involves multiple attentuation sites and a possible role for the ilvO locus which lies at the distal end of the ilvEDA operon (but is not part of it). Supportive evidence for the proposed direction of transcription was obtained by examination of a series of gammailv transducing phages.

Expression of a valine-resistant acetolactate synthase activity mediated by the ilv O and ilv G genes of Escherichia coli K-12

A strain carrying the ilv0603 mutation has been isolated in E. coli K-12 and its characteristics were found to be very similar to those previously reported by Ramakrishnan and Adelberg (1965a) for other ilv0 mutants. The strain carrying the ilv0603 mutation is resistant to valine inhibition (Valr) and we show that this resistance depends on the expression of a newly recognized gene, ilvG, which is located at min 75, between ilvE and ilvD on the E. coli K-12 map. The ilvG gene causes the expression of a Valr acetolactate synthase, which is detectable only when the ilv0603 mutation is also present in cis on the same chromosome. Under these conditions the Valr acetolactate synthase activity is eluted, on a hydroxylapatite column, at an ionic strength slightly lower than that required for elution of the remaining acetolactate synthase activity (sensitive to valine inhibition). The Valr peak is missing in a strain carrying an ilvG (amber) mutation.