Histone H1 Binding Does Not Inhibit Transcription of Nucleosomal Xenopus laevis Somatic 5S rRNA Templates

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Abstract
It has long been proposed that selective binding of histone H1 is, in part, responsible for the differential developmental regulation of the oocyte and somatic 5S rRNA genes in Xenopus laevis. In this study we show that histone H1 binds both oocyte and somatic genes equally after reconstitution into mononucleosomes or oligonucleosome arrays. Furthermore, we show that the binding of histone H1 selectively represses only oocyte gene transcription and that an RNA polymerase III transcription complex is able to initiate transcription of nucleosomal somatic templates regardless of whether histone H1 is present. These results support a model in which the differential regulation of the 5S rRNA genes is not simply due to the prevention of histone H1 binding by transcription complexes on the somatic genes, but rather to a difference in the histone H1 interaction with the somatic and oocyte genes.