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Category: Microbial Genetics and Molecular Biology; Bacterial Pathogenesis
Type IV Secretion Machinery, Page 1 of 2
< Previous page | Next page > /docserver/preview/fulltext/10.1128/9781555818395/9781555813017_Chap10-1.gif /docserver/preview/fulltext/10.1128/9781555818395/9781555813017_Chap10-2.gifAbstract:
This chapter provides an overview of the pathogenic involvement of Type IV secretion systems (T4SS), with a focus on the structural aspects and the molecular mechanisms of the type IV secretion process. The assembled knowledge gained from studies of individual secretion systems is used to propose a unified view of the architecture of the type IV secretion machinery at the molecular level. Different mechanistic aspects are discussed. T4SS are found predominantly in gram-negative bacteria. Exceptions are the bacterial conjugation systems of gram-positive bacteria and archaea with weak homology to the conjugation systems of gram-negative bacteria, which are regarded as the evolutionarily most ancient T4SS. The finding that relaxases are transferred to recipient cells independently of DNA transfer supports the view that the secretion machinery of bacterial conjugation systems transports the relaxase, which in turn trails the DNA and directs it into the target cell. Structural features of relaxases are discussed in the chapter. In T4SS, it is one of the three potential NTPases that are thought to energize the secretion process and/or the assembly of the secretion machinery. Recently, the crystal structures of a family of more widely distributed T4SS substrates, the conjugative relaxases, have been solved. Additionally, the pathway of a T4SS substrate that is always cotransferred with relaxases has been determined. The authors therefore confine themselves to describing the features of conjugative relaxases and the pathway of a relaxase-associated partner molecule, the T-DNA of A. tumefaciens.
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Electron microscopic image of P-pili. The image represents a section of an E. coli cell producing RP4-encoded P-pili. P-pili (arrowheads) are characteristically long and rigid and thus break off easily from the pilus-producing bacterium. When broken off, they assemble into large, filamentous bundles of pili (indicated by an arrow). Bar, 0.2 µm. This image was taken by Jana Haase and was provided by Gerhild Lüder and Rudi Lurz. Preparation and staining were as described previously ( Haase et al., 1995 ), using E. coli strain JE2571 harboring plasmids pML123 and pWP471.
Electron microscopic image of P-pili. The image represents a section of an E. coli cell producing RP4-encoded P-pili. P-pili (arrowheads) are characteristically long and rigid and thus break off easily from the pilus-producing bacterium. When broken off, they assemble into large, filamentous bundles of pili (indicated by an arrow). Bar, 0.2 µm. This image was taken by Jana Haase and was provided by Gerhild Lüder and Rudi Lurz. Preparation and staining were as described previously ( Haase et al., 1995 ), using E. coli strain JE2571 harboring plasmids pML123 and pWP471.