Figure 1.

Generation of the 55b deletion mutant. A) Map of the ~7kb slo transcriptional control region. Bent arrows on the line are transcription start sites for the five identified tissue specific core promoters that are named C0, C1, C1b, C1c, and C2. The gray boxes on the line are the first exon expressed from each core promoter. The short black box on the far right represents the first exon common to all slo transcripts. Red boxes below the line are short sequences conserved among Drosophila species. B) Homologous recombination strategy used to generate the transgenic lines slo^wΔ55b and slo^Δ55b. Homologous recombination between the replacement DNA (pink) and the chromosome (white) substitutes the 55b element with a floxed mini-white gene that is called slo^wΔ55b. Cre recombinase was used to excise the mini-white gene to produce the slo^Δ55b mutant allele. C) Genomic Southern blot analysis was used to confirm the procession described in B). Genomic DNA was digested with HindIII and Southern blot analysis was performed using a DIG-labeled probe that specifically recognizes the 3 kb upstream DNA sequence of 55b. Lane 1, DNA standard. Lane 2, DNA from wild-type flies displayed a ~5.2 kb HindIII band. Lane 3, DNA from a slo^wΔ55b homozygote that carries the mini-white insertion produces a band of ~10 kb. Lane 4, DNA from the slo^Δ55b produced by excision of the mini-white gene from the slo^wΔ55b allele generates a band of ~5.3 kb.