Figure 3.

Proposed model of molecular events involved in SLP gene cassette rearrangement by DNA inversion. DNA inversion between two oppositely oriented cassettes follows DNA strand exchange at the putative recombinase target site (∗) found upstream of each SLP gene cassette within the 5′ conserved region (small shaded box; ref. 8). Patterned boxes represent variable regions of SLP gene cassettes. A 6.2-kb intervening segment is topologically reversed, leading to ordered rearrangement of the SLP gene cassettes. Inversion of DNA segments containing the promoter (P over bent arrow) permits expression of alternate SLP gene cassettes (mRNA, arrow). Illustrated are inversion of the 6.2-kb promoter-containing element alone (Left), and the 6.2-kb element and one (Center) or two (Right) SLP gene cassette ORFs and the resultant genotypes. Each of these genotypes has been observed (Fig. 2D).