Figure 6.

Organization of the expression plasmid (top) and one archival plasmid (bottom) in B. hermsii. Two examples of vsp or vlp genes are denoted by “X” and “Y” and different fill patterns. There is a single expression site on one plasmid, and silent variants of vsp and vlp genes are found on the same and other plasmids. The direction and extent of transcription of the duplicate gene at the expression site is indicated by the arrow. The UHS element at the expression site comprises 61 nt around the start codon of the variant gene (Barbour et al., 1991a; Dai et al., 2006; Kitten et al., 1993). Silent genes vary in the extent to which their UHS regions are identical to the expression site UHS; this is represented here by the relative length of the UHS block. There is a 214 nt noncoding DHS element downstream from the expression site and adjacent to the plasmid telomere and at various locations on the plasmids. The lengths of vsp/vlp gene examples and the UHS and DHS elements are not to scale. (Courtesy of Alan Barbour, UC Irvine).