Figure 2.

Antigenic variation of Lyme borreliae VlsE and relapsing fever borreliae Vmp systems. (A) VlsE: the expression locus (vlsE) is located near the telomere (open oval) of linear plasmid (lp) 28-1 (blue or green arrow, promoter is indicated by a black arrow). Silent vls cassettes are located upstream and in the opposite orientation of vlsE. Antigenic variation occurs through the random and sequential insertion of silent cassette fragments (labeled 1, 2, and 3). (B) vlp (pink arrows) and vsp (purple arrows) cassettes are located throughout the genome on lp28-1, 28-2, 28-3, 28-4, and 32-1. The expression locus (blue or green arrow, promoter is indicated by a black arrow) is found on lp28-1 near the telomere (open oval). Changing the expressed Vmp cassette is achieved through deletion of the current cassette (blue arrow) followed by insertion of a copy of a new cassette (green arrow via recombination events) resulting in a change in the expressed Vmp on the surface of the bacterium (denoted by blue or green triangles, respectively). Gray arrows indicate non-Vmp ORFs; tan arrows indicate downstream homology sequences (DHS, sequences found throughout the genome and required for mapping recombination events at the Vmp expression locus).