NONHISTONE PROTEIN-1 (NHP1) IS A MEMBER OF THE KU PROTEIN FAMILY WHICH IS UP-REGULATED IN DIFFERENTIATING MOUSE MYOBLASTS AND HUMAN PROMYELOCYTES

We have previously purified and characterized a ubiquitous non-histone protein (NHP1) which has a high affinity (K-d 10(-11) M) for differen t avian vitellogenin gene sequences containing CpGs (Hughes et al. (19 89) Biochemistry 28, 9137-9142; Hughes and Jest (1989) Nucleic Acids R es. 17, 8511-8520). Here we show by microsequencing that the peptides derived from the purified p75 and p85 subunits of NHP1 from HeLa cells have between 64 and 100% identity with the human Ku autoantigen. Duri ng the differentiation of human HL-60 promyelocytes there is an increa se in the amount of p85 subunit protein whereas the level of the p75 s ubunit is unchanged. In differentiating mouse G8 myoblasts there is, h owever, an upregulation of both the p75 and p85 subunits and of the p8 5 mRNA. An inhibition of mouse myoblast differentiation by either cAMP , 3-aminohenzamide or sodium butyrate abolishes the upregulation of th e p85 subunit. In G8 myoblasts chemical, or physical stress by UV ligh t or X-rays does not upregulate the level of the p85 subunit. The poss ible involvement of NHP1 in the active demethylation of bifilarly meth ylated DNA will be discussed.