Glycogen satellite bands in isopycnic CsCl gradients

Sequence organisation in nuclear DNA from Physarum polycephalum. Interspersion of repetitive and single-copy sequences

Nuclear DNA from Physarum polycephalum is shown to contain three sequence components by reassociation kinetic analysis; a foldback component consisting of 6% of the DNA, a component with the properties of repetitive sequences comprising 31% of the DNA, and a majority component containing 63% of the DNA which reassociates with the kinetics characteristic of single-copy sequences. The complement of repetitive sequences is comprised of about 80 families of repeated elements, each containing approximately 1800 repeats per family. On average, these sequences are 6.4% richer in guanine and cytosine than total Physarum nuclear DNA. The repetitive sequences within a single family appear not to be identical, since on denaturation and annealing they give rise to collections of heteroduplexes less stable than native DNA. It is calculated that these duplexes are about 10% mismatched on average. Hydroxyapatite binding of DNA fragments of different sizes containing reassociated repeated elements demonstrates that these sequences are interspersed with single-copy sequences in a large portion of the Physarum genome. These observations are confirmed by direct examination of reassociated DNA using the electron microscope. In this manner it is shown that repetitive sequence elements possess a wide spectrum of lengths averaging 590 nucleotide residues, and they are separated by intervening segments of DNA about 930 residues in length.

Streptococcus mutans dextransucrase: functioning of primer dextran and endogenous dextranase in water-soluble and water-insoluble glucan synthesis

The extracellular enzyme activities of Streptococcus mutans 6715 that synthesize glucans from sucrose were concentrated and partially purified by ammonium sulfate precipitation and gel permeation column chromatography. Polyacrylamide gel analysis demonstrated that all of the major proteins precipitated by ammonium sulfate were quantitatively recovered in the high-molecular-weight, enzyme-containing aggregates found in the void volume of the gel column. Anion-exchange column chromatography was used to fractionate the aggregates into preparations, alpha and beta, which produced water-insoluble and water-soluble glucans, respectively. Polyacrylamide gel analysis showed that alpha and beta contained unique proteins and dextransucrase (EC 2.4.1.5) activities. Studies on the time course of glucan synthesis by alpha demonstrated that this enzyme preparation contained dextranase activity, which partially degraded nascent alcohol-insoluble glucan into alcohol-soluble products that were subsequently reincorporated into insoluble product. The beta enzyme preparation contained no detectable dextranase activity. Mixing experiments in the absence of primer dextran demonstrated that the dextranase activity present in alpha could modify glucan production by beta. CsCl density gradient analysis of product glucans demonstrated that exogenous primer dextrans were used as acceptor molecules by both the alpha and beta enzyme preparations, and that water-soluble glucans synthesized by beta could be converted into water-insoluble glucans by alpha. It is proposed that the structural heterogeneity of the native glucans produced from sucrose by S. mutans is a result of the concerted action of glucan-forming dextransucrases and endohydrolytic dextranase activity.

DNA base composition of some free-living nematode species

The mean base compositions (% GC) of DNA samples from five free-living nematodes were determined by CsCl equilibrium buoyant-density centrifugation and thermal denaturation studies. Both methods gave similar results indicating that there is no extensive replacement of the usual bases in nematode DNA. From the ultracentrifugation studies the % GC content of the DNA of Caenorhabditis briggsae (Dougherty and Nigon, 1949) Dougherty, 1953, Turbatrix aceti (Müller, 1783) Peters, 1927, Rhabditis (Rhabditis) anomala Hertwig, 1922 (Dougherty 1955), Panagrellus redivivus (Linn, 1767) T. Goodey, 1945, and Panagrellus silusiae (de Man, 1913) T. Goodey, 1945 was 36, 40, 42, 44 and 44, respectively.The sample of DNA from T. aceti showed two distinct ultraviolet absorbing bands in a CsCl gradient. The band at 1.688 g/cm3 proved to be a polysaccharide. It gave a distinctive refractive index pattern when viewed with the schlieren optical system, was insensitive to DNase treatment and was removed by a-amylase treatment. On the other hand, the material banding at 1.699 g/cm3 was shown to be DNA. This band produced no disturbance in the refractive index gradient. It was not altered by a-amylase treatment, but it was DNase sensitive.Since P. redivivus and P. silusiae were found to have the same DNA base composition their ability to interbreed was examined. These two forms were cross-fertile and the offspring were fully fertile.

Minor components of the DNA of Physarum polycephalum. Cellular location and metabolism

DNA metabolism in the slime mold Physarum polycephalum was studied by centrifugation in CsCl of lysates of cultures labeled with radioactive thymidine at various times in the cell cycle. During the G(2) (premitotic) phase of the cell cycle, two components of the DNA are labeled. One component is lighter (buoyant density 1.686 g/cc) than the mean of the principal DNA (1.700 g/cc), and one is heavier (approximately 1.706 g/cc). The labeled light DNA was identified chemically by its denaturability, its susceptibility to DNase, and the recovery of its radioactivity in thymine. Cell fractionation studies showed that the heavy and the principal DNA components are located in the nucleus and that the light DNA is in the cytoplasm. The light DNA comprises approximately 10% of the DNA. About (1/3)-(1/2) of the light DNA is synthesized during the S period, and the remainder is synthesized throughout G(2) (there is no G(1) in Physarum). The light DNA is metabolically stable. A low, variable level of incorporation of radioactive thymidine into the principal, nuclear DNA component was observed during G(2).