Further studies on satellite nucleoli in rat and mouse hepatocytes

To provide more information on satellite nucleoli, these nuclear structures were studied by means of cytochemical and immunofluorescence procedures in rat and mouse hepatocytes without and following experimental inhibition of the RNA synthesis. The immuno-staining specific for nucleoli or B23 as well as C23 proteins demonstrated that satellite nucleoli and characteristic nucleoli exhibit the same fluorescence. The number of satellite nucleoli decreased after inhibition of nucleolar RNA synthesis in a similar way to the number of silver-stained granules (SSGs) of characteristic nucleoli. Inhibition of RNA synthesis also reduced the number of hepatocytes containing satellite nucleoli. Thus, satellite nucleoli seem to be real nucleoli from single NORs which did not fuse in the formation of a characteristic nucleolus.     

Genetic transformation of Pseudomonas phaseolicola by R-factor DNA.

Summary The bacterium Pseudomonas phaseolicola was successfully transformed, for the first time, with R-factors RSF1010 and pBR322 DNA by a calciumshock and heat-pulse technique. Frequency of transformation for RSF1010 ranged from 0.8×10^-7 to 3.1×10^-6 and was ca. 0.4×10^-8 for pBR322.     

Autoradiographic studies of the replication of satellite DNA in the kangaroo rat. Autoradiographs of satellite DNA

Cells of the Kangaroo rat Dipidomys ordii contain large quantities of satellite DNA (Bostock et al., 1972). Radioactive DNA from such cells has been examined by autoradiography. After a long period of radioactive labeling, long tandem arrays of short radioactive pieces are suddenly observed which are attributed to the replication of satellite DNA. Autoradiograms of DNA isolated by CsCl density centrifugation from such lysates are in agreement with this hypothesis.This material is non-randomly distributed in lysates of single cells. The length of these pieces and their spacings are not remarkably different from DNA made earlier (presumably non-satellite DNA).     

Further studies on partially purified calf thymus DNA polymerase a.

Attempts to prevent the urea conversion of a 200-230,000 molecular weight DNA polymerase alpha to a 150-170,000 molecular weight form by the inclusion of protease inhibitors have not been successful. No other method has been found capable of dissociating a 50-70,000 fragment or subunit from the DNA polymerase subunit. Addition of this 50-70,000 subunit to the polymerase subunit does not aid the binding of the enzyme to DNA, but does have an effect on the utilisation of synthetic template-initiator complexes by the polymerase subunit.     

Methylation of satellite DNA

The lower amount of 5 methylcytosine in DNA from bull sperm relative to DNA of other bovine tissues is a result of the absence of this minor base from several of the satellite DNAs in sperm. This applies particularly to the 1.715, 1.711b and 1.709 satellites and less so to the 1.706 and 1.711a satellites. Mouse sperm DNA is also partially undermethylated.     

Further studies on phytoferritin

Summary Crystalline and paracrystalline inclusions found in plastids of willow cambium, grown under dim-light conditions, are considered to be phytoferritin. Phytoferritin is completely unaffected following treatment of cambial cells with deoxyribonuclease or ribonuclease, although other components are, at least in part, denatured. This is considered to exclude the possibility that the inclusions are viral particles. While not normally arranged in crystalline form, phytoferritin from embryonic axes of pea appears identical in structure with the complex found in cambial plastids. It, also, is not affected by treatment with nucleases for periods of up to 18 hours. Phytoferritin has been found only rarely in willow grown under conditions of high illumination.Four, five, or six electron-opaque subunits are most often found in the individual particles of phytoferritin. The most satisfactory explanation of the arrangements seen seems to be that the micellar configuration is in the form of an octahedron with a subunit at each of the six vertices.     

Further structural studies of zosterine

Traces of either ferrous or ferric salts greatly increase the rate of the stepwise degradation of reducing sugars by alkaline hydrogen peroxide, as measured by formation of formic acid; addition of larger proportions of iron salts causes relatively smaller effects. The results showed that, unless unusually strict precautions are taken to exclude traces of iron, the free-radical cleavage of the hydroperoxide adducts of reducing sugars is far more rapid than the ionic cleavage. The catalytic effect of iron salts is counteracted by addition of magnesium salts. With d-glucose, inhibition of the catalytic effect of iron by magnesium depends on both the magnesium-iron ratio and the concentration at a given ratio. Measurements with various molar proportions of the salts indicated that a magnesium-iron complex, containing six atoms of magnesium to one of iron, is formed. Presumably, removal of iron by formation of this complex inhibits the free-radical degradation of hydroperoxide adducts. In marked contrast to the results obtained with reducing sugars, the degradation of potassium glyoxylate and of glyoxal by alkaline hydrogen peroxide is extremely rapid, and not catalyzed by iron or inhibited by magnesium. The results are in accord with an ionic, rather than a free-radical, cleavage of the hydroperoxide adducts of these compounds. The rapidity of the ionic reaction may be attributed to the ready availability of an electron pair from the adjoining carbon atom.