[Stringent control of relA gene transcription in cells of Escherichia coli]. / "Strogii" kontrol' transkriptsii gena relA v kletkakh Escherichia coli.

Regulation of E. coli K12 relA gene transcription was studied. The rate of relA-RNA synthesis was measured by RNA-DNA-hybridization technique using cloned fragment of relA gene. Under seryl-tRNA deficiency the rate of relA-RNA synthesis was reduced six times in the strain CP78 (relA+) and only two times in its' relA-variant CP79. Chloramphenicol addition stimulated the rate of relA-RNA synthesis in starved relA+ cells. It was concluded that relA gene transcription is under "stringent control". The rate of relA-RNA synthesis increases proportionally with bacteria growth rate. Grown in glucose-minimal media strain with several copies of relA gene exhibits elevated ppGpp level (50 pmol/A450) and reduced rate of relA-RNA synthesis per one copy of relA gene. Thus, relA gene transcription is under negative regulation of ppGpp.

[Metabolic regulation of threonine operon transcription in E. coli cells]. / Metabolicheskaia reguliatsiia transkriptsii treoninovogo operona v kletkakh E. coli.

The threonine biosynthetic operon transcription in E. coli cells during balanced growth was studied. The rate of threonine-mRNA synthesis was measured by hybridization of impulse-labelled RNA with pYN 1107 DNA carrying the structural threonine genes A, B, C. It was shown that threonine-mRNA synthesis depends on bacterial growth rate being maximal at mu = 0.8 doublings per hour. The influence of the ppGpp on the bacterial growth rate and threonine-mRNA synthesis rate was demonstrated, using spoT-mutants and strains with several relA gene copies. The rate of threonine-mRNA synthesis is maximal at the ppGpp level of about 50-60 pmole/A450. The deviation from this ppGpp optimum level results in inhibition of the threonine-mRNA synthesis. Thus, ppGpp appears to be involved in metabolic regulation of operon transcription. A mechanism of negative regulation of threonine-mRNA synthesis by high concentrations of ppGpp is discussed.

[Study of the transmissibility of multiple drug resistance and the capacity to ferment lactose in a clinical strain of Kl. pneumoniae]. / Issledovanie transmissivnosti mnozhestvennoi lekarstvennoi ustoichivosti i sposobnosti fermentirovat' laktozu u klinicheskogo stamma pneumonirobial. Kl.

The donor properties of K. pneumoniae PI 220 with multiple drug resistance were studied. It was shown that the above strain carried 2 plasmids, i.e. R-plasmid pPI 220 controling resistance to ampicillin, streptomycin, tetracycline, chloramphenicol, kanamycin and sulphanylamides and plasmid pPI 221 controlling lactose fermentation. Both plasmids can be transfered on conjugation to strain E. coli P678 at a temperture of 28 degrees C at a rate of 10(-5) for pPI 220 and 10(-4) for pPI 221. The drug resistance controlled by pPI 221 was transfered mainly in a "blocks" simultaneously to 6 drugs. Deletion of plasmid pPI 220 was observed rarely. The donor properties of the strain were defined by the conjugative plasmid pPI 220 controlling the self-transfer and mobilization of plasmid pPI 221 incapable of the self-transfer. E. coli P678 (pPI 220) (PPI 221) acquired the donor properties and transfered both plasmids to E. coli J62 on crossing simultaneously at a rate of 10(-2), as well as to S. typhimurium LT2 and P. rettgeri at a rate of 10(-5). In all the recipient strains studied the transfered plasmids were unstable and segregated also simultaneously at a rate being the highest for P. retgari PI 230. The clones with stable preservation of the plasmids could be obtained by selection.