[Genetic mapping of transposon Tn5-induced mutation blocking threonine dehydrogenase in Escherichia coli K-12]. / Geneticheskoe kartirovanie indutsirovannoi transpozonom Tn5 mutatsii, blokiruiushchei treonindegidrogenazu u Escherichia coli K-12.

The paper deals with a mutant of Escherichia coli K-12 obtained by transposon Tn5 mutagenesis. Insertion of this transposon inactivated the gene for L-threonine dehydrogenase catalysing the first step of L-threonine degradation. The insertion of Tn5 was mapped by using conjugation as well as transduction by T4GT7 and P1. It is located at 81 min of the E. coli genetic map between mtl and pyrE genes.

[Funtional study of gene relA in the expression of amino acid operons. III. The effect of the allelic state of gene relA on the derepression of the threonine and isoleucine-valine operons of Escherichia coli K-12]. / Issledovanie funktsii gena relA v vyrazhenii aminokislotnykh operonov. Soobshchenie III. Vliianie allel'nogo sostoianiia gena relA na derepressiiu treoninovogo i izoleitsinvalinovogo operonov Escherichia coli K-12.

During the derepression of threonine and isoleucine-valine operons the increase of activity of homoserine dehydrogenase and threonine deaminase respectively occurs only in relA+ strains of Escherichia coli K-12, while the activity of these enzymes in relA mutants does not change. The increase of the activity of homoserine dehydrogenase in relA+ strains corresponds to the increase of the fraction of the thr-mRNA, i.e. the expression of threonine operon is regulated at the level of transcription. After isoleucine is exhausted, only relA+ cells of threonine producer MG442 increase homoserine dehydrogenase activity and production of threonine. Thus, the regulation of transcription and translation of threonine and isoleucine-valine operons depends upon the allelic state of the relA gene.

[Gene relA function in the expression of amino acid operons. I. Effect of the allelic state of gene relA on phenotypic manifestations of auxotrophic threonine and isoleucine mutations in Escherichia coli K-12]. / Issledovanie funktsii gena relA v vyrazhenii aminokislotnykh operonov. Soobshchenie 1. Vliianie allel'nogo sostoianiia gena relA na fenotipicheskoe proiavlenie mutatsii auksotrofnosti po treoninu i izoleitsinu u Escherichia coli K-12.

The substitution of the relA gene mutant allele with wild type allele of this gene in strictly auxotrophic strain of Escherichia coli K-12 GT25, carrying thr B1007 mitation, results in the appearance of the partial dependence of the bacterial growth upon threonine. On the other hand, the introduction of relA mutation into genome of incomplete threonine auxotroph, which was isolated as pseudorevertant from the strict threonine auxotroph CP78, recovered the strict dependency of the growth on the presence of threonine in the medium. The introduction of relA mutation into genome of partial isoleucine auxotroph, carrying a mutation in ilvA gene, reduces the residual activity of threonine deaminase under the conditions of derepression and results in the appearance of strict dependency of bacterial growth on the presence of isoleucine. These data indicate that operons, which control the biosynthesis of threonine and isoleucine, are positively regulated by the product of relA gene. The possibility of using leaky mutations, which lead to incomplete block of these amino acids synthesis, for testing allelic state of relA gene is discussed.

[Gene relA function in the expression of amino acid operons. II. Effect of the allelic state of gene relA on the overproduction of threonine by an Escherichia coli K-12 mutant resistant to beta-hydroxynorvaline]. / Issledovanie funktsii gena relA v vyrazhenii aminokislotnykh operonov. Soobshchenie II. Vliianie allel'nogo sostoianiia gena relA na sverkhsintez treonina mutantom Escherichia coli K-12 ustoichivym k beta-oksinorvalinu.

Mutants, resistant to threonine analogue, DL-alpha-amino-beta-hydroxyvaleric acid, were obtained after the treatment of Escherichia coli K-12 RelA- cells with nitrosoguanidine, and among them the strain with maximal threonine production (about 3g/l) was selected. Genetic and biochemical analysis of the producer has revealed the dependency of the threonine production on at least three mutations. The mutation in the thrA gene disturbs retroinhibition of homoserine dehydrogenase by threonine. The mutation in the ilvA gene decreases the activity of threonine deaminase, and thus results in partial isoleucine auxotrophy, and finally, the reversion in the relA gene restores the stringent amino acid control of RNA synthesis in threonine producer cells. The role of relA gene in threonine production was demonstrated by comparing pairs of strains differing from one another in the allelic state of the relA gene. The level of threonine synthesis (its intra- and extracellular concentrations) during moderate isoleucine starvation in RelA+ cells 2-3 times as high as in RelA- cells. The presence of relA+ allele is found to result in the increase of the cell resistance to DL-alpha-amino-beta-hydroxyvaleric acid.

[Intracellular pool of free amino acids in a wild strain of Corynebacterium glutamicum and its lysine-producing mutants]. / Vnutrikletochnyi fond svobodnykh aminokislot Corynebacterium glutamicum shtamma dikogo tipa i ego mutantov, produtsiruiushchikh lizin.

The intracellular content of free amino acids was measured in the wild-type strain of Corynebacterium glutamicum 13032 and its lysine producing mutants 410 and 133, resistant to the combined effect of threonine and S-2-aminoethyl cysteine, a lysine analog. After 18- and 48-hour cultivation of all strains the major components of the amino acid pool were glutamic acid, alanine and lysine, and those of the cell-free supernatant were alanine and lysine. After 18-hour cultivation the lysine content in mutants was 2-3 times higher than in the wild-type strain. After 48-hour cultivation the lysine content in mutants remained unchanged and in the wild-type strain increased. After 18- and 48-hour cultivation the lysine content in the supernatant of mutants was 15 and 33 times higher than in that of the parental strain. These findings are compared with the activities of aspartokinase from Cor. glutamicum 13032, 410 and 133.

[Effect of amino acids on the beta-aspartokinase activity from Corynebacterium glutamicum of wild and mutant strains]. / Vliianie aminokislot na aktivnost' beta-aspartokinazy Cory nebacterium glutamicum shtamma dikogo tipa i ego mutanta.

The effect of amino acids, their structural analogs and ammonium sulphate on the enzyme activity of beta-aspartokinase isolated from Corynebacterium glutamicum was studied. Two strains were used: one of the wild type and the other--a mutant strain whose growth remains uninhibited by a simultaneous addition of threonine and S-2-aminoethylcysteine, a lysine analog. Significant differences in the effect of amino acids and their analogs on the beta-aspartokinase activity of the parental and mutant strains were detected. These findings suggest that the lysine supersynthesis by the mutant strain of Corynebacterium glutamicum occurs due to genetically induced changes of allosteric properties of the mutant enzyme.

[Characteristics of lysine transport in a wild type strain and lysine-producing mutant of Corynebacterium glutamicum]. / Osobennosti transporta lizina v kletki shtamma Corynebacterium glutamicum dikogo tipa i lizinprodutsiruiushchikh mutantov.

An active transport system high specific for 1-lysine was found in the cells of the wild strain of Corynebacterium glutamicum, Km being about 10 microM. Accumulation of lysine was higher, if the cells were cultivated on a medium containing glucose. The cells of the homoserine-deficient lysine producer have no alterations in the lysine transport. The lysine transport was also studied in three lysine producing analog resistant mutants (two mutants are resistant to aminoethylcysteine and one to lysine hydroxamate). The key enzyme of the lysine biosynthesis, aspartate kinase, is insensitive to the feedback inhibition by the mixture of lysine and threonine in all the mutant studied; at the same time the cells of these mutants grown on a glucose-containing medium above mentioned alterations are suggested to provide the resistance to the lysine analog.