The effects of cortisol on transfer ribonucleic acid methylase activity and protein metabolism in cancer tissue [proceedings].

after ["PIP, administration in vivo in Go-phase or early G,-phase. Gel electrophoresis showed that the nucleosomes recovered in the chromatin from the phosphorylated nuclei contained both mononucleosomes with 200-base-pair DNA and histone HI and core particles with 140-base-pair DNA and no histone H1. ["PIP, uptake into histones H3 and H2A occurred only in the latter (Table 1). Using rats of over 350g body wt., which are presumed to have considerable amounts of heterochromatin in their livers even at the peak of DNA synthesis, it was possible to obtain 140-base-pair particles and mononucleosomes from nuclei after micrococcal nuclease digestion, which were enriched with respect to new DNA and histones, compared with nucleosomes retained in the nuclear pellet after lysis. Model studies with normal rat liver nuclei phosphorylated in vitro indicated that the released core particles containing phosphorylated histone H2A and probably ADP-ribosylated histone H3 had lost their ADP-ribosylated histone H1, which is more easily dissociated from incubated nuclei than unmodified histone H1 (Caplan et a / . , 1978). Core particles and mononucleosomes from partially hepatectomized rats in S-phase also contained phosphorylated histones. We conclude that interbody regions associated with ADP-ribosylated histone HI are especially prone to attack from micrococcal nuclease. In nuclei with substantial amounts of heterochromatin, hindrance to the release of 'mononucleosomes' and higher nucleosomes from the condensed regions results in a preferential release of phosphorylated and/or newly replicated mononucleosomes during digestion and subsequent lysis.