Transcriptional Regulation of Mouse Ribosomal RNA Synthesis by Pathways Involving Protein Kinase C, Calcium, Insulin and Serum

We probed individual regions of the rDNA gene of Mouse Macrophage J774. A1 tissue culture cells for transcriptional Activity by using nuclear run- on assays. we determined that the intergenic spacer-region IGS, the external transcribed sequences ETS, and the 23S regions of the rDNA gene are transcribed and apparently under regulatory control, both in cells that are rapidly growing in 10 Fetal bovine serum supplemented media and in slower growing cells in 2 fetal bovine supplemented media The IGS region of the RDNA is transcribed at approximately 2 of the rate of the ETS region. The ENH region of the RDNA gene is transcribed at a low rate, which did not change when cells were stimulated with TPA A23187, insulin, or serum. The ETS region was transcribed at approximately 20 of the rate of the 28S region. These observations suggest processing of the rDNA transcripts from the ETS region occur rapidly in intact cells, of that the structural regions of the gene 18S, 5.8S, and 28S are transcribed at a higher rate than the ETS region. We demonstrate that transcription occurs upstream of the spacer promoter.