Figure 5.

Three mechanisms for serotype switches by B. hermsii: allelic replacement, intramolecular DNA rearrangement, and in situ promoter activation. The different mechanisms are discussed in the text. P indicates the promoter and the location of the expression site near the right telomere of a linear plasmid; an overhead arrow shows whether the gene is active and the direction of transcription. vsp and vlp genes at the expression site location or in archival locations on the same (squiggly line background) or another linear plasmid (white background) are schematically represented by different patterns and grayscale values. The serotype of the cell, similarly indicated by pattern or grayscale, corresponds to vsp or vlp gene, at the expression site. In the second mechanism a deletion by direct repeats (small white horizontal bars) occurs and results in a non-replicative circle. (Courtesy of Alan Barbour, UC Irvine).