Age-dependent deamidation of H1° histones in chromatin of mammalian tissues

Abstract: The composition of the H1° histone subfractions was examined in different rat and mouse tissues. Using reverse-phase HPLC and hydrophilic-interaction liquid chromatography we have found that the relative proportions of all four forms of H1° differ from tissue to tissue and from species to species. In principle, we observed an age-dependent increase in the amount of both the N-terminally acetylated (H1°a Asn-3 and H1°a Asp-3) and the deamidated forms of H1° (H1°a Asp-3 and H1°b Asp-3). Compared with the proportion of N-terminally acetylated H1° forms in liver, kidney and brain of rats and mice 20 days of age, we found an increase in these H1° subfractions of up to 30% in the corresponding organs of 300-day-old animals. The proportion of deamidated H1° forms was 1.6- to 4-fold higher in the livers and 8- to 12-fold higher in the brains of 300-day-old mice and rats, respectively, than in 20-day-old animals. The tissue-specific nature of the ratio of H1° subfractions suggests that the different forms of histone H1° have specific individual functions. The possible biological significance of age-related accumulation of N-terminal acetylated and deamidated histone H1° forms is discussed in the light of our results.