Fig. 7. A model for da transcriptional regulation. (A) Wild-type transcriptional regulation of da depends on both positive and negative control. An ovary-specific enhancer that is required for initiation of transcription in the somatic ovary is located within the 1.5 kb da intron. The location of this enhancer must be downstream of the dalyh insertion site (indicated in B) and also within the sequence included in the da.G32 promoter reporter transgene (extents indicated by the HindIII and BglII sites). Within this region (500 bp into the intron), a STAT-binding site is one enhancer candidate. At least in this tissue, the initial expression of da leads to the production of Da protein, which subsequently acts to maintain the transcription of da. The binding partner of Da for this autoregulation is not known; however, numerous target E-box-binding sites (E) are dispersed throughout the genomic sequence. To keep da transcript levels from becoming too high, there is also a negative regulatory element, which must be located downstream of the dalyh insertion site. (B) In the dalyh allele, a springer retrotransposon acts as a transcriptional insulator that is capable of blocking the effects of both the positive and negative regulatory elements without disrupting Da autoregulation. In most tissues, the function of this allele appears to be normal, indicating that there is generally no problem with its transcriptional activation. In the somatic ovary, however, transcriptional activation fails because the promoter is insulated from the downstream ovary enhancer. But, dalyh can be transactivated by Da protein from another allele. The springer element also insulates the negative regulatory element, so that the amount of da transcript produced from the dalyh allele is higher than that from a wild-type allele. The insulating effects of springer depend on the Su(lyh) gene product. By analogy to Su(Hw)-mediated gypsy insulation, Su(lyh)-mediated insulation may result from direct binding of the Su(lyh) protein to springer sequences.