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Role of Nonhistone Chromosomal Proteins in the Regulation of Histone Gene Expression¹

Department of Biochemistry and Molecular Biology, University of Florida, Gainesville, Florida 32610[G. S. S., J. L. S., J. A. T., W. D. P., R. L. J.], and Division of Biological Sciences, University of Michigan, Ann Arbor, Michigan 48104 [L. J. K.]

Histone gene expression was studied during the cell cycle of continuously dividing HeLa S₃-cells and following stimulation of confluent monolayers of WI-38 human diploid fibroblasts to proliferate. The presence of histone messenger RNA (mRNA) sequences was assayed by hybridization to a ³H-labeled single-stranded DNA complementary to histone mRNA's. In HeLa S₃-cells, histone mRNA sequences were found in the nucleus and associated with polyribosomes during S phase but not during G₁. Transcripts of S-phase chromatin contained histone mRNA sequences but those of G₁ chromatin did not. Similarly, in WI-38 cells association of histone mRNA sequences with polyribosomes and transcription of histone mRNA sequences from chromatin parallel DNA replication. Together these results suggest that the regulation of histone gene expression resides, at least in part, at the transcriptional level. Chromatin reconstitution studies provide evidence that nonhistone chromosomal proteins play a key role in activation of histone gene transcription during the period of the cell cycle when DNA is replicated. Phosphate groups associated with the S-phase nonhistone chromosomal proteins appear to be functionally involved in the control of histone gene readout. Although WI-38 human diploid fibroblasts transformed by SV40 exhibit morphological and biochemical modifications characteristic of neoplastic cells, transcription of histone mRNA sequences remains unaltered.

¹ Presented at the Conference, "Regulation of Gene Expression in Development and Neoplasia," June 2 to 5, 1976, Santa Ynez, Calif. These studies were supported by research grants from the National Science Foundation (GM38349, BMS75-18583, and BMS74-23418), the NIH (GM20535), and the American Cancer Society (F73UF-6 and F75UF-4).

² Presenter.