Fig. 1. BR-C protein is not detected at Sgs loci or at transposed copies of the Sgs4 regulatory region. Salivary gland polytene chromosomes were immunostained with anti-BR-C antibody SA 4256 (red) and counterstained with the DNA dye Hoechst 33258 (green). In the bottom panels of B,C, DNA and immunostaining are merged to allow proper localization of the immunofluorescent signals. (A) Staining of chromosomes of the wild-type strain Oregon R (ORN) and the BR-C null mutant npr1³. The antibody specifically detects BR-C protein in the wild-type chromosomes but not in the npr1³ chromosomes. (B) Sections of Oregon R wild-type chromosomes 1 (X), 2L and 3L, which contain the loci of five Sgs genes, Sgs4 (3C11), Sgs1 (25B2-3), and Sgs3, Sgs7 and Sgs8 (68C). Neither of the Sgs loci coincides the strong fluorescent signals, which are abundant on all chromosomes. (C) Staining of a wild-type fourth chromosome (ORN) and a fourth chromosome of a transformant line (T4) that carries four copies of the Sgs4 regulatory region inserted at 102 D3-5. The intensity of the immunofluorescent signal at 102 D is not changed in the presence of the insertion.