Replicative form sedimentation

FIGURE 7.4. Effect of intercalation on the sedimentation coefficient of X 174 replicative form, (a) Ethidium bromide (72% closed circles) (b) proflavin (67% closed circles) (c) actinomycin (75% closed circles). Open circles replicative form open triangles nicked DNA Hr dye bound/nucleotide. (From Ref. 10.)... 

DNA-dependent RNA synthesis in E.coli cells was inhibited under experimental conditions by actinomycin D. After 50-90 sec, almost 70% of the of the parent RNA was found in one fraction of RNA with a sedimentation coefficient of about 20S, which these workers called the replicative form of RNA, because it was resistant to ribonuclease (double-helical form). The quantity of P of ribonuclease-resistant RNA then fell sharply, and a new peak of this RNA appeared after 3.5 min (Fig. 12). In one case this wave of change of the parent RNA into the double-helical RNAase-resistant form was observed on four successive times. In addition, slight but definite incorporation of parent P material was observed into a special low-molecular weight 6S fraction (mol.wt. from 1 to 30 X10 ) was observed, which, however, contained much newly synthesized RNA (in this fraction the ratio of parent RNA/new RNA was much lower than in the 2OS fraction of RNA). 

A dynamic coupled-column liquid chromatographic technique was used to obtain aqueous solubility data on 11 aromatic hydrocarbons. The aqueous solubility at 25° C was determined for each compound. The precision of replicate solubility measurements was better than 3%. The variation of the solubility of each compound with temperature is expressed in the form of either a quadratic or cubic equation based on a least-squares fit of the solubility to temperature. These equations can be used to interpolate the solubility to within 2% of the experimentally measured values between 5° and 30°C. Enthalpies of solution (AHJ were then calculated from the values obtained and Setschenow constants were calculated from the effect of salinity on solubility. This system was also used to investigate the partitioning of PAHs between aqueous solutions and some sediment samples. 

When rat pancreatic polynucleosomes were poly(ADP-ribosylated) with purified calf thymus poly(ADPR) polymerase and examined by electron microscopy a relaxation of their native zigzag structure was observed, even at high ionic strengths they showed a close resemblance to chromatin depleted of histones HI. The relaxed state of poly(ADP-ribosylated) polynucleosomes was also confirmed by sedimentation velocity analysis [19, 20]. Locally relaxed regions can also be generated within poly-nucleosome chains by the activity of their intrinsic poly(ADPR) polymerase and appeared to be correlated with the formation of hyper(ADP-ribosylated) forms of histone HI and an increase of DNA polymerase activity [21]. The posttranslational transitory modifications of histones are potential modulators of chromatin stmcture. This may be involved in DNA transcription, replication, and repair. 

The effect of polycations on the viability of E. coli and on the adsorption of RNA to E. coli was analyzed (Koch and Vollertsen, unpubhshed). Exposure of a growing culture of E. coli MRE 600 to different concentrations of DEAE-dextran (20 to 100 (xg/ml) inhibits the replication of E, coli. This effect is completely reversible. On dilution or after sedimentation of the cells and resuspension in fresh medium, growth resumes at a rate comparable to that obtained in a control culture (Fig. 17). Furthermore, the ability of E. coli to form colonies is not reduced by exposure of the cells to DEAE-dextran or to other polycations (Lempidakis and Koch, 1972). 

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