The HSPA1A transgene association with nuclear speckles is promoter dependent. (A, top left) Plasmid pSP14-MT2A + HSPA1A containing the MT2A promoter driving the HSPA1A gene and a 64-mer lac operator repeat. (bottom left) Transgene nuclear speckle association indexes for five independent cell clones before (ctrl) or after zinc induction. (right, top row) RNA FISH (red) before (left) and after (right) zinc induction; DAPI DNA counterstaining (blue). (right, bottom row) SC-35 staining (red) before (left) and after (right) zinc induction. (B) The corresponding layout as in A, but for plasmid pSP14-HSPpro + MT2A containing the HSPA1A promoter driving the MT2A gene. (C) Combined RNA FISH SC-35 immunostaining for cell clone pSP14-HSPpro + MT2A_C1. Transgenes were labeled with EGFP-LacI (left), RNA FISH signal (second from left), SC-35 staining (second from right), and merged image (right). Bars, 2 µm. Error bars show SEM.