The release of chromatin template restrictions by natural polyribonucleotides

Differential effects of heparin on replicative DNA synthesis and unscheduled DNA synthesis

The effect of heparin on DNA synthesis was compared between replicative DNA synthesis and unscheduled DNA synthesis. Replicative DNA synthesis in permeable cells or nuclei prepared from rapidly growing mouse ascites sarcoma cells was inhibited by heparin. Unscheduled DNA synthesis in nuclei isolated from normal rat liver or from mouse ascites sarcoma cells in stationary phase was stimulated by heparin at low concentrations but inhibited by high heparin concentrations. DNA polymerase activity assayed with activated calf thymus DNA and DNA polymerase alpha purified partially from mouse ascites sarcoma cells was inhibited with either calf thymus histones or heparin. DNA synthesis inhibited with histones was partially reactivated by heparin. Replicative DNA synthesis in permeable cells was inhibited by adding histones to the assay mixture, and the inhibited DNA synthesis was partially reactivated by low concentrations of heparin. These results indicated that the replicated sites (or replication machinery) in permeable cells or nuclei were largely unrestricted by histones and that heparin inhibition of replicative DNA synthesis was due to the direct inhibitory interaction of heparin with some essential component(s), such as DNA polymerase, of replication machinery.

Action of heparin on mammalian nuclei. I. Differential extraction of histone H1 and cooperative removal of histones from chromatin

Heparin interacts strongly with the histone component of chromatin, forming heparin-histone complexes which resist dissociation by 0.2 M H2SO4. Heparin treatment of unfractionated histones isolated from nuclei of Chinese hamster cells indicates that the affinities of the histone classes for heparin appear in the order from greatest to least: (H3, H4) greater than (H2A, H2B) greater than H1. However, when isolated nuclei are treated with heparin, H1 is released from the chromatin more readily than the other four histone classes. The release of these four histones (H2A, H2B, H3, and H4) is coordinate and occurs in a highly cooperative manner, as indicated by (1) dependence of the initial kinetics of histone removal upon heparin concentration, (2) analysis of DNA and histones in the fractions obtained from differential sedimentation of heparin-treated nuclei, and (3) analysis of the products from heparin-treated nuclei by equilibrium centrifugation in metrizamide density gradients. The results suggest rapid procedures for using heparin as an agent for studying the accessibility of histones in chromatin of intact nuclei. The relationship of these results to current models of chromatin structure is discussed.

Effects of polyamines and methylglyoxal bis(guanylhydrazone) on hepatic nuclear structure and deoxyribonucleic acid template activity

1. The interaction of polyamines and methylglyoxal bis(guanythydrazone) (1, 1'-[(methylethanediylidene)-dinitrilo]diguanidine) with isolated rat liver nuclei was investigated by electron microscopy. 2. At 4mM, putrescine was without effect; however, spermidine, spermine or methylglyoxal bis(guanythydrazone) resulted in dispersed chromatin and alterations in nucleolar structure. In addition, spermidine or methylglyoxal bis(guanylhydrazone) caused marked aggregation of interchromatin granules. 3. The DNA template property of calf thymus DNA was examined by using DNA polymerases from Escherichia coli, Micrococcus lysodeikticus and calf thymus in the presence of 0-5 mM-amine. 4. In the presence of DNA polymerase, spermine or methylglyoxal bis(guanylhydrazone) inhibited activity, whereas putrescine or spermidine had much less effect or in some cases stimulated [3H]dTMP incorporation. 5. Template activity which was inhibited by spermine or methylglyoxal bis(guanylhydrazone) could be partially restored by additional DNA or enzyme. 6. When mixed with calf thymus DNA, calf thymus histone inhibited template activity as measured with E. coli DNA polymerase. The template activity of such a 'histone-nucleate' could not be restored by putrescine, spermidine, spermine or methylglyoxal bis(guanylhydrazone). 7. DNA template activity of isolated rat liver nuclei was tested by using E. coli DNA polymerase. None of the amines was able to increase the template activity of the nuclear DNA in vitro.

Pineal protein kinase: effect of enzymic phosphorylation on actinomycin D binding by, and template activity of, chromatin

The ability of protein kinase from bovinepineal gland to phosphorylate calf-thymus chromatin and thereby to alter the association between chromatin DNA and histones was investigated. Phosphorylation of calf-thymus chromatin by pineal protein kinase results in an apparent decreased binding between the histones and DNA in chromatin, as indicated by (i) an increase in actinomycin D-binding sites after phosphorylation and (ii) an increase in the template capacity of the calf-thymus chromatin after phosphorylation. F(1) histone and F(3) histone are the major histone classes in the chromatin that are phosphorylated by the protein kinase. These results support the hypothesis that pineal protein kinase may function at the transcriptional level.

Stimulation of Sendai virion transcriptase by polyanions

Exogenous polyribonucleotides stimulated the ribonucleic acid (RNA) transcriptase in Sendai virions. Added yeast RNA, polyadenylic acid, or polycytidylic acid increased incorporation of (3)H-guanosine monophosphate as much as fivefold. The products of stimulated reactions were virus-specific as determined by hybridization with Sendai virion RNA, but they sedimented more slowly (13s) than the product of an unstimulated reaction (16s). The stimulating activity was nondialyzable and heat stable, but was abolished by alkaline hydrolysis. Nucleoside monophosphates, individually or in combination, were ineffective, confirming the requirement for a polymer. Among other substances tested for effects on Sendai virion transcriptase, polyaspartic acid and polyglutamic acid stimulated the enzyme; polyinosinic acid, polyuridylic acid, and polyamines had no effect; and dextran sulfate and polyvinyl sulfate were inhibitory.

Structural alteration in isolated rat liver nuclei after removal of template restriction by polyanions

Specific polyanions release DNA template restrictions for DNA synthesis in isolated rat liver nuclei. The degree to which DNA synthesis is enhanced can be correlated with a spectrum of changes in nuclear structure Each polyanion which is effective in the release of template restriction produces a characteristic alteration in nuclear ultrastructure. Polyanions which have no effect on DNA synthesis do not appear to cause any change in nuclear organization or ultrastructure. Parallel measurements of nuclear DNA release and nuclear volume changes also indicate that template-activating polyanions cause remarkable changes in the structural organization of the treated nuclei. These results indicate that DNA template activation involves direct interactions between polyanions and nuclear constituents and suggest the possibility that naturally occurring polyanions might have a role in the control of gene activity