PHOSPHORYLATION OF SYNTHETIC ACIDIC PEPTIDES BY CASEIN KINASE-II - EVIDENCE FOR COMPETITION WITH PHOSPHORYLATION OF PROTEINS INVOLVED IN TRANSCRIPTION

Phosphorylation of several synthetic acidic peptides by biochemically isolated casein kinase II (CKII) and by cellular and nuclear extracts containing CKII-like activity has been investigated. Especially the sy nthetic peptide pyroGlu-Asp-Asp-Ser-Asp-Glu-Glu-Asn comprising the car boxy-terminal acidic hepta-peptide of the largest subunit of RNA polym erase II was found to serve as an excellent substrate for purified CKI I. Moreover, this peptide reduces the rate of 'in vitro' ATP-dependent stimulation of DNA transcription induced by the proteins in the extra cts. Since the peptide itself is also significantly phosphorylated in such assays, it is supposed that it serves as a competitive substrate for the phosphorylation of proteins in the extracts whose phosphorylat ion seems to be a prerequisite for their activity in the transcription process. This points to the involvement of CKII and substrate(s) of C KII in the process of transcription.