Analysis of RNA transcription from isolated mouse liver chromatin has been undertaken by means of RNA-excess hybridizations with small amounts of radioactive DNA. This analysis indicates that mouse liver chromatin is a restricted template for the in vitro synthesis of RNA complements to repetitive DNA, but more RNA species are synthesized than are found in the RNA isolated from mouse liver nuclei. Extraction with 0.5 M NaCl destroys the template restriction of isolated chromatin. RNA synthesized in vitro from DNA or chromatin templates by Escherichia coli RNA polymerase, as well as in vivo mouse liver nuclear RNA, were each hybridized to125I-labeled DNA of high, intermediate, or low reiteration frequency. Chromatin-primed and nuclear RNA saturate a smaller portion of each DNA fraction than does DNA-primed RNA. However, chromatin-primed RNA saturates more high and low reiteration frequency DNA than does nuclear RNA. Simultaneous hybridization of nuclearand chromatin-primed RNA with 125I-labeled DNA indicates that chromatin-primed RNA contains all of the sequences present in nuclear RNA. Extraction of chromatin with 0.5 M NaCl leads to removal of histone F1, as well as a wide variety of non-histone proteins. When used as a template for in vitro RNA synthesis, such salt-extracted chromatin produced RNAs that hybridize as large a portion of each DNA fraction as does DNA-primed RNA.
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