Fig. 7.

Summary of integration sites near tRNA genes in dictyostelid genomes. The topology of RNA polymerase III transcription factors TFIIIC and TFIIIB on a tRNA gene is shown as deduced by Male et. al. [69]. The composition of TFIIIB in three subunits is inferred by the presence of orthologs of TBP, Brf1 and Bdp1 in all dictyostelid species. TFIIIC is a six-subunit factor that consists of two subcomplexes, τA and τB [69]. Note that TFIIIB subunit Bdp1 may enter the transcription complex only transiently by displacing TFIIIC subcomplex τB [69]. In dictyostelid genomes only the most conserved TFIIIC subunits τ131 (TFC4) and τ95 (TFC1) can be identified by homology to either yeast or human orthologs. The schematic is not drawn to scale. The tRNA gene, including its internal regulatory sequences (A box and B box), is indicated as a gray bar. Integration windows in tRNA gene-flanking regions of six different dictyostelid retrotransposon families are indicated. Note that DGLT-A and NLTR-B belong to different retrotransposon classes and therefore independently developed a similar integration behavior upstream of tRNA genes. The same is true for TRE3 and Skipper-2 elements, which target similar regions downstream of tRNA genes