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Biomedical subjects

D J Cummings

Publications and source records attributed to D J Cummings.

At least 73 records · Page 4Linked to original sources
PubMed1975

Studies on Macronuclear DNA from Paramecium aurelia.

Macronuclear DNA was isolated from purified macronuclei of Paramecium aurelia and the size distribution was determined with regard to growth phase and method of extraction. DNA molecules as long as 105 microns and as short as 0.2 microns were observed. It was concluded that the method of extraction affected the observed length of DNA extracted and that macronuclear DNA isolated from cells in balanced growth was less susceptible to nuclease degradation than was DNA isolated from cells in stationary phase. Renaturation studies were performed on macronuclear DNA and a kinetic complexity of 22-times E. coli DNA was determined. This value was similar to those values reported for Tetrahymena and Stylonychia macronuclear DNA. Correcting for GC base content yielded a kinetic complexity for Paramecium macronuclear DNA of 11-times E. coli DNA which corresponded to 3 X 10(10) daltons. There would be about 1400 copies of a unit genome of this complexity within each newly replicated macronucleus. Density gradient analysis indicated that the genes coding for ribosomal RNA had a greater density in CsCl than the bulk DNA. Molecular hybridization studies indicated that the genes coding for 25 S RNA represented 0.14 percent of the total macronuclear DNA. Correcting for GC base content, this corresponded to 30-35 25 S RNA genes per unit genome. These results on Paramecium are discussed in relationship to other ciliate macronuclear DNA.

Animals↗
PubMed1975

DNA-dependent DNA polymerase activities from Paramecia macronuclei.

Three DNA-dependent DNA polymerase activities, A, B, and C, have been detected from the macronucleus of Paramecium. The enzymes were separated and partially purified by DEAE-cellulose and phosphocellulose chromatography. These three enzymes can be further distinguished from each other by the effect of KCl, araCTP and different DNA templates on their activities. All three enzymes have the same molecular weight (900 000-110 000), are dependent on Mg2+ and added DNA template and are inhibited by sodium pyrophosphate. The relative amounts of the three enzyme activities vary with the growth stage of the Paramecia from which they are isolated. In balanced growth, three polymerase activities (A, B AND C) are observed, whereas in late log or stationary phase polymerase C is absent, while the level of polymerase B decreases by a larger factor than polymerase A. These results have been related to the possible functional roles of the three activities and their relationship to activities in other organisms studies is discussed.

Animals↗
PubMed1975

Canavanine-mediated depletion of polyamine pools in Escherichia coli: effect of head morphogenesis and DNA synthesis.

We have found that L-canavanine inhibited the synthesis of polyamines in T4-infected Escherichia coli. These polyamines are known to be required for T4 DNA synthesis and may be involved in phage morphogenesis. The new data indicate that the inhibition of polyamine synthesis is not primarily responsible for the L-conavanine-mediated inhibition of DNA synthesis nor does it seem to be involved in the induction of lollipops. L-Canavanine does influence the relative amounts of putrescine and spermidine found in the phage particle, but it does not influence the amount of DNA phosphate neutralized by polyamines.

Arginine↗
PubMed1975

Structural aberrations in T-even bacteriophage. VII. In vitro analysis of the canavanine-mediated inhibition of proteolytic cleavage.

Canavanine arrests a critical function in head morphogenesis and the potential for forming giant T-even phage particles termed lollipops is induced. Formation of the particles requires the addition of arginine and the restoration of normal functions. We now report on an investigation into the effects of canavanine on both the T4-induced proteolytic activity and on the substrate proteins. Using an in vitro cleavage assay we have shown that the gene 21-dependent proteolytic activity from canavanine-treated extracts is markedly inhibited, whereas the substrate proteins retain a high susceptibility for cleavage. The proteolytic activity in extracts treated with canavanine followed by arginine is readily detectable, and proteins previously synthesized in the presence of canavanine can be cleaved. Protein synthesis is apparently required for the appearance of the proteolytic activity after the canavanine-arginine treatment. Mixing experiments suggest the requirement for a component of the gene 21-dependent proteolytic activity that is not coded for by gene 21.

Arginine↗
PubMed1974

Structural aberrations in T-even bacteriophage. IV. Parameters of induction and formation of lollipops.

Previous results from our laboratory have shown that when a T-even bacteriophage-infected bacterial cell was exposed to l-canavanine followed by an l-arginine chase, a monster phage particle, termed a lollipop, was formed. We now describe certain parameters concerning (i) the induction and (ii) the formation of T4 lollipops. The induction step involves a T4 late function, and can require only a 3-min exposure to l-canavanine. Short pulses of l-canavanine result in the formation of shorter lollipops indicating the presence of a possible "precursor substance" which is influenced by l-canavanine. DNA synthesis is inhibited by l-canavanine but is stimulated 20 to 40 min after the addition of l-arginine. Chloramphenicol prevents both responses indicating a possible protein involvement. The appearance of lollipops and phage was noted only after 25 min after the addition of l-arginine.

Arginine↗
PubMed1974

Structural aberrations in T-even bacteriophage. V. Effects of canavanine on the maturation and utilization of specific gene products.

Previous results have shown that when a T-even bacteriophage-infected cell was exposed to l-canavanine followed by an exposure to l-arginine, a monster phage particle, termed a lollipop, was formed. l-Canavanine was necessary for the induction event but l-arginine was required for the maturation of the particle. We now describe the effects of canavanine on the maturation of certain T4 proteins and their role in the induction of lollipops. The cleavage reactions of the head proteins P22, P23, P24, and IPIII are prevented by l-canavanine as shown by the accumulation of the precursor proteins and the failure of the cleaved products to appear. l-Canavanine also prevents the appearance of P12 (tailplate protein) and P20 (head protein) indicating that these proteins may undergo a proteolytic cleavage during normal assembly. The formation of P10 (tailplate protein) and P18 (tail sheath protein) is also affected by l-canavanine. The data suggest that P23 in conjunction with P20 plays a major role in the determination of the length of the phage head.

Autoradiography↗
PubMed1973

Protein synthesis and deoxyribonucleic acid-membrane attachment during thymineless death in Escherichia coli.

The proteins synthesized during thymineless death in Escherichia coli B and B/r were analyzed by polyacrylamide gel elctrophoresis. It was found that the amount of a protein of molecular weight 80,000 to 88,000 is greatly increased during thymineless death compared to the amounts of other cell proteins. A technique for the isolation of cell membrane-deoxyribonucleic acid (DNA)-nascent ribonucleic acid (RNA) complex on detergent crystals was used to determine whether DNA might be detached from the cell membrane as a result of thymineless death. It was found that under no conditions of thymineless death or immunity to thymineless death was there any change in the attachment of DNA or pulse-labeled RNA to cell membrane.

Bacterial Proteins↗