Location of RNA polymerases by nuclear run-on. (A) A map of the fragments that were analyzed is shown; the Sμ repetitive region (RR) was not analyzed. Position 1 corresponds to nt 135,091 in GenBank/EMBL/DDBJ under accession no. AC073553. The restriction sites ScaI (S), EcoRI (E), and HindIII (H) are depicted. The bent arrow shows the position of the Iμ promoter. The region forming the proposed R-loops is indicated. For graphs in B–D, representative blots for each graph are shown on the right. The intensity of hybridization of labeled nascent RNA to each of the fragments was graphed based on the value of β-actin, which was set as 1. γ-Actin and CD3δ were positive and negative controls, respectively. (B) Ung^−/− splenic B cells before and after stimulation with LPS and IL-4. The error bars represent the SD of the values from triplicate blots from one experiment on days 0 and 2 with five mice. Three independent experiments with five mice each were performed and showed similar patterns and intensities. (C) Aid^−/−Ung^−/− cells after stimulation. Data are from triplicate blots from one experiment with three mice, with error bars showing SD. Three independent experiments with three mice each were performed with similar results. (D) Sμ del cells after stimulation. The ΔS probe corresponded to the 5′ and 3′ ends flanking the 3.7-kb deletion (16). Data are from triplicate blots from one experiment with three mice. Error bars indicate SD.