Possible specific activation of RNA synthesis in PC-12 cell isolated nuclei by small acidic peptides.

Three synthetic peptides, pyro-Glu-Ala-Gly-Glu-Ser-Glu-Asp (Pep A), pyro-Glu-Ala-Gly-Glu-Glu-Glu-Ser-Asn (Pep B), and pyro-Glu-Asp-Asp-Ser-Asp-Glu-Glu-Asn (Pep C), bear sequences possibly belonging to components of a naturally occurring family of strongly related small acidic chromatin peptides involved in regulation of gene expression. In a crude nuclear fraction and in purified nuclei from PC-12 cells, Pep A and Pep B activate RNA synthesis, specifically acting on the RNA polymerase II transcription system. On the other hand, Pep C shows an inhibitory effect on RNA synthesis in purified nuclei but an activation in the crude nuclear fraction. Control experiments show that the serum thymic factor does not affect RNA synthesis in the crude nuclear fraction or in purified nuclei. A possible regulation by peptide phosphorylation via casein kinase II (more active in purified nuclei than in the crude nuclear fraction) is discussed.