Components and features of the SNB. (A) RNA-binding domains of SNB components. Numbers represent the amino acid counts of each protein. (B) Immunofluorescence analysis of SNB components and the effect of RNase treatment. Five SNB components colocalized in SNBs, and all protein signals dispersed upon RNase treatment (+RNase). (C) SNB formation requires RNAPII transcription. Immunofluorescence analysis of SNB components was performed in HeLa cells treated with actinomycin D (Act D; 0.03 and 0.3 µg/ml) or DRB (100 µM). The control cells were treated with DMSO. (D and E) A temperature shift reversibly regulates SNB formation. The temperature for cell culture was shifted from 37°C to 32°C, and cells were incubated for 24 h (D). The cells were incubated at 32°C for 24 h, shifted to 37°C, and incubated for 1 or 3 h (E). SNBs were detected by immunofluorescence labeling of Sam68, HNRNPD, and HNRNPL. The cell populations (%) in which each protein and Sam68 or HNRNPL signals overlap are shown in B, C, D, and E (>100 cells, n = 3). Bars, 10 µm.