[Identification and expression of plasmid genes participating in the synthesis of microcin C51]. / Identifikatsiia i ékspressiia plazmidnykh genov, uchastvuiushchikh v sinteze mikrotsina C51.

A structural gene of heptapeptide, which is a component of the microcin C51 molecule, was identified by hybridization of plasmid DNA fragments and a mixture of synthesized oligonucleotides with the sequence corresponding to that of amino acids in the peptide. Sequence analysis of the structural gene of microcin peptide and its promoter region was performed. The data obtained indicate that the peptide of microcin C51 is synthesized on ribosomes. Four polypeptides of 67, 39, 16, and 14 kDa were identified using the system of minicells. These polypeptides are specified by a DNA fragment responsible for microcin synthesis and immunity in a producer cell. Apparently, three of these polypeptides with molecular masses of 67, 39, and 16 kDa are responsible for microcin production and immunity. The 67 kDa polypeptide is involved in the expression of immunity to microcin and, probably, in microcin production.

[Cloning and analysis of genetic determinants determining the production of microcin B2 and B27]. / Klonirovanie i analiz geneticheskikh determinantov, opredeliaiushchikh produktsiiu mikrotsinov B2 i B27.

Cloning of plasmid genes for the synthesis of two peptide broad-spectrum antibiotics-microcins B2 and B27- and for host cell immunity to their action was performed. Recombinant plasmids containing these genes were designated pBE108 and pVB27, respectively. Deletional derivatives of plasmid pBE108 and mutant plasmids were obtained via transposon Tn5 insertions, which did not determine production of microcin B2 and immunity to it. Phenotypic study and physical mapping of these plasmids demonstrated that a 4.2-kb DNA fragment is responsible for B2 microcin production; immunity is provided by a 1.4-kb DNA fragment. A 5-kb DNA fragment is necessary for microcin B27 synthesis and expression of immunity to its action. Homology between these fragments and with plasmid DNA for the synthesis of microcin B17 and immunity to it was found. Homology between plasmid genes determining synthesis of type B and C microcins and host cell immunity to them was not observed. The production of B27 microcin is controlled by the product of the ompR gene; B2 microcin synthesis does not depend on this product. The mutations recA and lexA increase the susceptibility of Escherichia coli cells to the action of microcins B2 and B27 but not microcin C51.

[Plasmid genes participating in the synthesis of microcin C51]. / Plazmidnye geny, uchastvuiushchie v sinteze mikrotsina C51.

Microcin C51 is an antibiotic with a wide application range produced by Escherichia coli cells. Using insertions of transposon Tn5 a set of mutations was induced in the recombinant plasmid pAST, which determines synthesis of microcin C51. The mutations were physically mapped. Complementation analysis was performed for insertions and deletions in the Mic+ plasmids pAST and pUHAB that lead to the absence of microcin or immunity to it. The analysis showed that at least three plasmid genes take part in microcin production and two genes determine immunity of producer cells to microcin. Functioning of the ompR gene product was necessary for synthesis of microcin C51.

[Characterization of enterobacteria producing the broad-spectrum antibiotics microcins]. / Kharakteristika énterobakterii, produtsiruiushchikh antibiotiki shirokogo spektra deistviia mikrotsiny.

As a result of screening among 11956 enterobacteria strains isolated from feces of normal children, grown-ups and lambs, seven active microcin-producing strains were obtained. The microcins were shown to be peptides or their derivatives with a low molecular weight (less than 10,000) and a broad spectrum of activity, mainly against gram-negative bacteria. According to cross immunity criteria the microcins studied belonged to two different types. Those of type I could be further classified into two subtypes on the account of difference in the spectrum of antibacterial activity. In 5 cases out of 7 the microcin-producing ability and immunity to microcins have been attributed to plasmids that the strains harboured. The effect of microcins on sensitive cells depended on ompR and ompF gene products.

[The role of peritoneal macrophages in realizing the growth inhibiting effect of glucocorticoids on reinoculated murine hepatoma 22 cells: the effect of hydrocortisone on the cytotoxic activity and metabolism of phospholipids by macrophages]. / Rol' peritoneal'nykh makrofagov v realizatsii rost-ingibiruiushchego deistviia gliukokortikoidov na kletki perevivaemoi myshinoi gepatoma 22: vliianie gidrokortizona na tsitotoksicheskuiu aktivnost' i obmen fosfolipidov makrofagov.

A single injection of hydrocortisone to rats with ascite hepatoma 22 had practically no effect on tumour growth. Inhibition of tumour growth was observed only after reinoculation of ascite hepatoma to mice that had received no less than 8 daily injections of the hormone. A single injection of hydrocortisone induced inhibition of the cytotoxic activity and decreased phospholipid metabolism in peritoneal macrophages. Contrariwise, long-term administration of the hormone caused marked activation of macrophage cytotoxicity. In this case incorporation of 32P into macrophage phospholipids was restored up to the control level. It is concluded that one of mechanisms underlying the inhibitory effect of glucocorticoids on macrophages is inhibition of phospholipid turnover. Presumably, long-term administration of the hormone promotes the formation of a new population of macrophages insensitive to the inhibitory effect of glucocorticoids and possessing a high cytostatic activity. The appearance of such activated macrophages may account for the enhancement of hydrocortisone effect on tumour cells upon prolonged administration of the hormone.