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. Author manuscript; available in PMC: 2016 Apr 25.
Published in final edited form as: Trends Microbiol. 2003 Nov;11(11):527–535. doi: 10.1016/j.tim.2003.09.004

Figure 2.

Figure 2

Conservation of type IV secretion genes. The Agrobacterium tumefaciens VirB–D4 reference system is a type IVA secretion system composed of 11 VirB proteins (Mpf) and the VirD4 T4CP (type IV coupling protein), whereas the Dot–Icm, R64 and ColIb-P9 systems are representatives of the type IVB subclass. Dot–Icm proteins discussed in the text or related to VirB proteins are identified. Genes encoding protein homologs are shown. These are not necessarily in the order found in the respective genomes. Homologs of the VirB4 ATPase and VirB7 through to VirB10 are postulated to comprise an ancestral ‘core’ structure to which function-specifying subunits or protein subassemblies were added to evolve the present-day family.