FIG. 1.

Setup of the TRE trap. The D. discoideum gene encoding UMP synthase (pyr5-6) is equipped with an intron derived from the D. discoideum cbfA gene (2). The intron sequence is indicated as a dashed line. The white arrow indicates the transcription orientation of the pol III gene inserted into the intron. All tested pol III genes were inserted into the trap as EcoRI fragments, schematically exemplified by D. discoideum Val^UAC. TRE5-A integrations into the trap were isolated by PCR using pyr5-6 exon-specific primers as indicated. The tRNA gene-internal A-box and B-box promoter elements are indicated. Mutations introduced into the consensus GTCnnnnG⁵³TTC⁵⁶RANYC⁶¹ B-box motif of the D. discoideum Val^UAC tRNA gene are indicated.