Figure 1.

(A) Outline of the SNRPN transcription unit indicating regions deleted in AS and PWS patients (ASSRO and PWSSRO, shaded boxes; refs. 10–12). The PWSSRO has been narrowed down recently to ≈3 kb (T. Ohta and R. D. Nicholls, personal communication). Exons are shown as black boxes. Filled and open lollipops in the region of the SNRPN CpG island (open box) represent maternally methylated NotI sites (32). Fragments investigated in this study (PWSPX and PWSDS) are indicated. (B) Schematic outline of the PWSPX transgene. A GAL4 binding cassette (black and white box) immediately 5′ to the promoter mediates binding of the activating protein. The direction of transcription is indicated by arrowheads. Open boxes below the construct denote CpG islands as determined by standard procedures (33) by using grail (34). (C) Quantitative determination of lacZ expression in GAL4-induced transgenic larvae carrying the PWSPX fragment or a control fragment from the nonimprinted EXT1 locus. (D) Quantitative determination of mini-white expression in adult transgenic flies carrying a sequence from the Drosophila Pc locus or a sequence from the human APP locus immediately 5′ to mini-white. Error bars indicate the SD; numbers indicate distinct independent strains.