Effects of spermine and sodium butyrate on the in vitro phosphorylation of HMG non-histone proteins of the liver of young and old rats.

The in vitro phosphorylation of high mobility group (HMG) proteins and its modulation by spermine and sodium butyrate were studied in the liver of young (15 week) and old (138 week) male rats. Except HMG 1 which remained unchanged, the phosphorylation of other proteins (HMG 2, 14 and 17) decreased drastically in old age. Spermine stimulated the phosphorylation of HMG 1 and 17 in young but HMG 1, 2 and 14 in old rats. The incorporation of (32)P into total HMG proteins was enhanced by butyrate in the liver of both ages. However, the degree of stimulation was higher in young rats. Particularly, the HMG 1 and 17 of young and HMG 2 and 17 of old rats showed increased phosphorylation. Furthermore, butyrate also inhibited the phosphorylation of HMG 2 in young and HMG 1 and 14 in old rats. Such alteration in the phosphorylation of major HMG proteins modulates their interaction with DNA and other components of chromatin. This may account for changes in the higher order organization of chromatin and expression of genes during aging.