DNA polymerase activities in Tradescantia paludosa pollen grain nuclei

DNA-polymerase activity detected in situ. Relationship between incorporation of 3H-deoxytriphosphates and 3H-actinomycin D binding during the cell cycle in antheridial filaments of Chara vulgaris L. Effect of auxin and cytokinins

DNA-polymerase activity during the cell cycle (S + G2 + M + C type) in antheridial filaments cells of Chara vulgaris was studied using the autoradiographic method. Incorporation of 3H-deoxytriphosphates (3H-dTPs) during the whole of interphase indicates, that the cell cycle is not accompanied by distinct changes in enzyme activity. Incorporation of 3H-dTPs was also observed in spermatids and in early stages of spermatogenesis. Intensity of 3H-dTPs incorporation during interphase and spermatogenesis is similar to the intensity of 3H-actinomycin D (3H-AMD) binding. Auxin (IAA) and kinetin stimulate both 3H-AMD binding and 3H-dTPs incorporation; benzyladenine does not affect any of these processes. The in situ autoradiographic method of detecting DNA-polymerase activity reveals availability of DNA template for the enzyme rather than DNA polymerase activity itself.

Chromatin-bound DNA polymerase from higher plants : A DNA polymerase-β-like enzyme

Chromatin-bound DNA polymerase has been extracted from pea (Pisum sativum L.) seedlings, and partially purified by solubilization from chromatin followed by chromatography on columns of either DEAE-cellulose or DEAE-Sephadex. The enzyme elutes from DEAE-cellulose as a single peak, but is fractionated into two peaks, CI and CII, by DEAE-Sephadex chromatography. If the enzyme is stored at-15°C for several days prior to chromatography, a third peak, CIII, derived from CII, is obtained. The polymerase is devoid of nuclease activity, and is relatively insensitive to N-ethyl-maleimide. These features, taken with the ion requirements and with data obtained from other plant species, lead to the suggestion that the chromatin-bound DNA polymerase of higher plants is similar to the DNA polymerase-β from vertebrates.

A permeable cell system for studying DNA replication in synchronized HeLa cells

Treatment of HeLa cells with a hypotonic buffer solution makes them permeable to nucleotides. Cells which are in S-phase at the time of treatment continue to synthesize DNA when supplied with the four deoxyriboside triphosphates, ATP, Mg2+, and the proper ionic environment. DNA replication extends from sites which were active in the cells prior to treatment. The product is confined to the nucleus and is sensitive to deoxyribonuclease. Under optimum conditions, up to 5% of the HeLa genome can be replicated from exogenous nucleotides. In synchronized cultures the level of DNA replicase activity, as measured in permeable cells at different points in the cell cycle, correlates with the rate of [14C] thymidine incorporation measured in the living, untreated cells.

Development of chromatin-bound and soluble DNA polymerase activities during germination of Pisum sativum L

Chromatin-bound and soluble DNA-dependent DNA polymerases were assayed in the embryonic axes of germinating peas (Pisum sativum L.). Activities of both enzymes increased markedly during germination, prior to the onset of net DNA synthesis. The activity of the soluble polymerase showed a better temporal correlation with net DNA synthesis than did the activity of the chromatin-bound polymerase. The activity of the soluble polymerase greatly exceeded the activity of the chromatin-bound polymerase, particularly during the period of DNA replication.

The activity of deoxyribonucleic acid polymerase in some species of algae

1. The activities of DNA polymerase preparations from the algae Euglena gracilis, Chlamydomonas reinhardtii, Chlorella pyrenoidosa, Anabaena variabilis and Anacystis nidulans were measured. The blue-green algae Anabaena and Anacystis contain a 5-20-fold higher activity of the enzyme than do the green algae. DNA polymerases from the blue-green algae show a pH optimum of 9 and prefer a relatively low Mg(2+) concentration (1-3mm). DNA polymerases from the green algae, however, display a pH optimum between 7.5 and 8.5 and an optimum Mg(2+) concentration of 8mm. With all algae, a higher polymerase activity was obtained with denatured salmon sperm DNA as template than with native DNA. All four deoxyribonucleoside 5'-triphosphates must be present for full activity of the polymerases. 2. With one exception, the deoxyribonuclease activities in the preparations, measured under conditions of the DNA polymerase assay, are low compared with corresponding preparations from Escherichia coli. Chlamydomonas extracts contain a high deoxyribonuclease activity. 3. After purification on columns of DEAE-cellulose, the polymerase activity was linear over a wide range of protein concentrations, except for Chlamydomonas preparations, where the observed deviation from linearity was probably attributable to the high nuclease activity. 4. DNA polymerases from all these algae bind strongly to DNA-cellulose; 6-40-fold purifications of the enzyme were obtained by chromatography on columns of DNA-cellulose. 5. The partially purified polymerases of Euglena and Anacystis are heat-labile but become much more heat-stable when tested in the presence of DNA.