RESUMO
pSAM2 is an 11 kb integrative element from Streptomyces ambofaciens that is capable of conjugal transfer. A system based on differential DNA modification by SalI methyltransferase was used to localize pSAM2 in the donor or recipient strain, and thus to determine the various steps associated with transfer. Initiation (i.e. excision and replication of pSAM2 in the donor) occurs a few hours after mating with a recipient strain. pSAM2 replicates in the recipient strain, spreads within the mycelium and then integrates into the chromosome. Transfer generally involves single-stranded DNA. In Streptomyces, only a few genes, such as traSA for pSAM2, are required for conjugal transfer. Using the differential sensitivity to the SalI restriction-modification system of transfers involving single- and double-stranded DNA, we found that pSAM2 was probably transferred to the recipient as double-stranded DNA. This provides the first experimental evidence for the transfer of double-stranded DNA during bacterial conjugation. Thus, TraSA, involved in pSAM2 transfer, and SpoIIIE, which is involved in chromosome partitioning in Bacillus subtilis, display similarities in both sequence and function: both seem to transport double-stranded DNA actively, either from donor to recipient or from mother cell to prespore.
Assuntos
Conjugação Genética , Elementos de DNA Transponíveis/genética , Fator sigma , Streptomyces/genética , Fatores de Transcrição , Proteínas de Bactérias/genética , Proteínas de Bactérias/metabolismo , DNA Bacteriano/genética , DNA Bacteriano/metabolismo , Escherichia coli/genética , Escherichia coli/fisiologia , Dados de Sequência Molecular , Streptomyces/fisiologia , Transformação BacterianaRESUMO
pSAM2, a 10.9-kb mobile integrative genetic element from Streptomyces ambofaciens, possesses, as do a majority of Streptomyces conjugative plasmids, a kil-kor system associated with its transfer. The kor function of pSAM2 was attributed to the korSA gene, but its direct role remained unclear. The present study was focused on the determination of the KorSA targets. It was shown that KorSA acts as a transcriptional repressor by binding to a conserved 17-nucleotide sequence found upstream of only two genes: its own gene, korSA, and pra, a gene positively controlling pSAM2 replication, integration, and excision. A unique feature of KorSA, compared to Kor proteins from other Streptomyces conjugative plasmids, is that it does not directly regulate pSAM2 transfer. KorSA does not bind to the pSAM2 genes coding for transfer and intramycelial spreading. Through the repression of pra, KorSA is able to negatively regulate pSAM2 functions activated by Pra and, consequently, to maintain pSAM2 integrated in the chromosome.
Assuntos
Elementos de DNA Transponíveis/genética , Proteínas Repressoras/metabolismo , Streptomyces/metabolismo , Sequência de Bases , Sítios de Ligação , Pegada de DNA , Elementos de DNA Transponíveis/fisiologia , DNA Bacteriano/genética , DNA Bacteriano/metabolismo , Deleção de Genes , Regulação Bacteriana da Expressão Gênica , Marcação de Genes , Genes Bacterianos/genética , Genes Bacterianos/fisiologia , Dados de Sequência Molecular , Ligação Proteica , Proteínas Repressoras/genética , Homologia de Sequência do Ácido Nucleico , Streptomyces/genética , Transcrição GênicaRESUMO
Acute eye and upper respiratory irritation was reported at an industrial facility that processes green salads in water containing hypochlorite. The irritant agents were chloramines resulting from the reaction of hypochlorite and nitrogen compounds coming from the sap proteins released when the vegetables were cut. Specific sampling and analytical methods were developed in order to assess the workers' exposure. Monochloramine, dichloramine and nitrogen trichloride were found in the atmosphere, which can explain the irritation phenomena of which the workers complained. In the washing room (where salads are processed), the total chloramine concentration ranged from 0.4 to 16 mg.m-3, depending on the day and the location of the area sampling points. The exposure of workers determined by personal sampling ranged from 0.2 to 5 mg.m-3. In a previous study, with swimming pool instructors exposed to the same pollutants, irritation phenomena generally appeared at chloramine values of around 0.5 mg.m-3.
