RESUMO
Bacteria of the genus Streptomyces have a linear chromosome, with a core region and two 'arms'. During their complex life cycle, these bacteria develop multi-genomic hyphae that differentiate into chains of exospores that carry a single copy of the genome. Sporulation-associated cell division requires chromosome segregation and compaction. Here, we show that the arms of Streptomyces venezuelae chromosomes are spatially separated at entry to sporulation, but during sporogenic cell division they are closely aligned with the core region. Arm proximity is imposed by segregation protein ParB and condensin SMC. Moreover, the chromosomal terminal regions are organized into distinct domains by the Streptomyces-specific HU-family protein HupS. Thus, as seen in eukaryotes, there is substantial chromosomal remodelling during the Streptomyces life cycle, with the chromosome undergoing rearrangements from an 'open' to a 'closed' conformation.
Assuntos
Cromossomos Bacterianos/fisiologia , Streptomyces/genética , Streptomyces/fisiologia , Proteínas de Bactérias/genética , Proteínas de Bactérias/metabolismo , Divisão Celular , DNA Bacteriano , Regulação Bacteriana da Expressão Gênica , Hifas/genéticaRESUMO
Variation in growth rate has provided a basis for the broad classification of Mycobacterium: (i) the slow-growing class includes the human pathogens Mycobacterium tuberculosis and M. leprae, and (ii) the fast-growing class includes saprophytic nonpathogens, such as M. smegmatis. An intimate association between DNA chromosomal replication and growth rate have been suggested. However, the molecular basis of this relation is unknown. In this article, we summarise our recent work on the study of the origin replication region of some species of mycobacteria, determination of the factors regulating the initiation of DNA replication and the characterisation of the main factor of the replicative machinery, the DnaA protein.
Assuntos
Cromossomos Bacterianos/fisiologia , Replicação do DNA/fisiologia , DNA Bacteriano/fisiologia , Mycobacterium/genética , Proteínas de Bactérias/genética , Cromossomos Bacterianos/genética , Replicação do DNA/genética , DNA Bacteriano/genética , Proteínas de Ligação a DNA/genética , Mycobacterium/crescimento & desenvolvimentoRESUMO
The bacterial genome is present in the cell within a complex structure, the nucleoid. The nucleoid contains the genomic DNA, and molecules of RNA and proteins. The main proteins of the nucleoid are: RNA polymerase, topoisomerases and the histone-like proteins: HU, H-NS (H1), H, HLP1, IHF and FIS. The DNA molecule in the nucleoid is under helical tension or supercoiling and is organized into 43 +/- 10 topodomains. DNA supercoiling is generated by the activity of the topoisomerases and by DNA-protein interactions. In this review, we analize current knowledge in Escherichia coli about genome organization and proteins of the nucleoid.
Assuntos
Cromossomos Bacterianos , Proteínas de Bactérias/genética , Proteínas de Bactérias/metabolismo , Membrana Celular/fisiologia , Membrana Celular/ultraestrutura , Cromossomos Bacterianos/fisiologia , Cromossomos Bacterianos/ultraestrutura , DNA Topoisomerases Tipo I/genética , DNA Topoisomerases Tipo I/metabolismo , DNA Topoisomerases Tipo II/genética , DNA Topoisomerases Tipo II/metabolismo , DNA Bacteriano/genética , DNA Bacteriano/metabolismo , DNA Bacteriano/ultraestrutura , DNA Super-Helicoidal/genética , DNA Super-Helicoidal/metabolismo , DNA Super-Helicoidal/ultraestrutura , RNA Polimerases Dirigidas por DNA/genética , RNA Polimerases Dirigidas por DNA/metabolismo , Escherichia coli/genética , Escherichia coli/ultraestrutura , Genoma Bacteriano , Histonas/genética , Histonas/metabolismo , Poliaminas/metabolismoRESUMO
The Escherichia coli rap mutant does not support the growth of bacteriophage lambda (D. Henderson and J. Weil, Virology 71:546-559, 1976). We located the rap site at 26 min in the E. coli genetic map and determined the gene order fadR-rap-supF-trp from our transduction experiments. Plasmid pHO1 harbors a 5.6-kilobase-pair segment of the E. coli chromosome which contains the pth gene (B. Hove-Jensen, Mol. Gen. Genet. 201:269-276, 1985). This plasmid complemented rap bacteria, suggesting that it carries the dominant allele rap+. Subcloning experiments reduced the rap-complementing segment to 1.5 kilobase pairs. This segment still contained pth; thus, both loci are tightly linked. The lit mutations that inhibit phage T4 growth in E. coli are located nearby at 25 min (W. Cooley, K. Sirotkin, R. Green, and L. Snyder, J. Bacteriol. 140:83-91, 1979). We showed that rap and lit mutations are phenotypically and genetically different.