Our major objective is to elucidate factors involved in the interaction of the histone proteins with chromatin both in concert with DNA replication as in S phase cells and when DNA replication is absent as in G1 and quiescent or G0 cells. We have developed methodology which allows us to study soluble histone not bound to chromatin and alterations in the level of soluble histone in different cell growth states and during changes in the rates of protein or DNA synthesis. Recently we published a model which suggested that level of soluble histone was involved in the balancing of histone and DNA synthesis. In contrast to earlier ideas, this model viewed the level of soluble histone as instrumental in the stabilization of histone mRNA when protein synthesis was inhibited as well as in its destabilization when DNA synthesis was inhibited. Results of kinetic studies of soluble histone currently in press show that there are multiple kinetic components. Overall the results are consistent with the previously proposed model. Presently, these kinetic studies are being extended to include quiescent cells. Two other directions are being pursued. The first direction is the characterization of soluble histone H1; this study has required some changes in our methodology. H1 is of interest because it binds to the outside of the nucleosome and has been implicated in the transcriptional repression of certain genes. The second direction, which should lead to the next major phase of our investigations of histone metabolism, is to isolate and characterize factors which interact with soluble histone using typical biochemical techniques and assays developed during the kinetic studies.
