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. 2010 Nov;2(11):a000299. doi: 10.1101/cshperspect.a000299

Figure 1.

Figure 1.

Schematic comparison of the flagellum and type III injectisome of Salmonella. (A) Schematic overview of the flagellum of Salmonella. The structure of the flagellum consists of three parts: 1) a basal body with a flagellar-specific type III secretion system within the inner membrane ring; 2) a flexible hook acting as a universal joint to 3) the rigid filament. Dashed boxes illustrate proteins with functions in flagellar type III secretion. Also indicated are FlgM, the negative regulator of late substrate gene expression that is secreted after hook-basal-body secretion, and the hook-length regulator FliK that measures rod-hook length and ultimately determines the secretion substrate specificity switch. OM = outer membrane; PG = peptidoglycan; IM = inner membrane. The inlay EM (electron micrograph) picture shows an isolated hook-basal-body complex of Salmonella (Thomas et al. 2001). (B) Schematic overview of the SPI-1 injectisome of Salmonella. Many components of the flagellum and injectisome are structurally and/or functionally related. The injectisome structure can also be divided into three main parts: 1) the basal body with the type III secretion apparatus within the inner membrane ring; 2) a straight needle connecting the bacterial secretion system to 3) the translocon complex that forms a pore in the membrane of eukaryotic host cells. The inlay EM picture shows an injectisome of Salmonella enterica (Marlovits et al. 2004). (The arrows on this image served in the original paper to explain aspects of the reconstruction procedure.) (A [inlay], Reprinted, with permission, from Thomas et al. 2001 [© ASM]; B [inlay] reprinted, with permission, from Marlovits et al. 2004 [© AAAS].)