A MITOGEN-STIMULATED AND ANISOMYCIN-STIMULATED KINASE PHOSPHORYLATES HMG-14 IN ITS BASIC AMINO-TERMINAL DOMAIN IN-VIVO AND ON ISOLATED MONONUCLEOSOMES

The rapid, transient induction of 80-100 immediate-early (IE) genes up on mitogenic stimulation occurs irrespective of protein synthesis and is mediated by modification of existing proteins. Two mechanisms, not mutually exclusive, involving modification either of sequence-specific transcription factors or of structural chromatin proteins primed by p re-association with responsive effecters are conceivable. Here, we sho w that upon IE gene induction, the non-histone high-mobility-group pro tein HMG-14, but not the related protein HMG-17, becomes serine phosph orylated in its basic, amino-terminal region close to where it binds n ucleosomal DNA. Phosphorylation, normally transient, occurs independen t of transcription and is quantitative and prolonged during superinduc tion. Brief micrococcal nuclease digestion substantially releases HMG- 14 from nuclei in the mononucleosome-bound state. Finally, mononucleos omes prepared from mitogen-stimulated, but not control, cells contain a mitogen-activated kinase that phosphorylates HMG-14 in vitro on the same site(s) as in intact cells. The association of HMG-14 and its mit ogen-activated kinase with nuclease-sensitive mononucleosomes has impl ications for models of mitogen-stimulated IE gene induction.