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D R Zusman

Publications and source records attributed to D R Zusman.

84 records · Page 5Linked to original sources
PubMed1978

Chromosome replication in Myxococcus xanthus.

The rates of DNA synthesis during the cell-division cycle were measured in Myxococcus xanthus growing in three different media permitting a twofold variation in doubling time. In all three media, simple DNA cycles were observed. Synthesis of DNA occurred during 85% of the cell-division cycle, independent of generation time, from 5 to 11 h. Cells were observed to contain one bacterial nucleoid at birth that later divided synchronously midway through the cell cycle. Nucleoid segregation appeared to begin before chromosome replication was completed. The DNA content of exponential-phase bacteria was determined to be about 20 +/- 3 X 10(-9) microgram per cell; newborn bacteria contained about 14 +/- 2 X 10(-9) microgram of DNA per cell. Exponential-phase bacteria showed about a 50% increase in DNA in the presence of chloramphenicol (50 microgram/ml). The number of randomly segregating chromosomes present in exponential-phase bacteria was determined by following the fate of prelabeled DNA during outgrowth in nonradioactive media. The results are consistent with a model in which cells are born with exactly one complete unreplicated chromosome. The molecular weight of such a chromosome is about 8.4 +/- 1.2 X 10(9).

Cell Cycle↗
PubMed1978

Changes in cyclic AMP levels during development in Myxococcus xanthus.

Cyclic AMP levels doubled in Myxococcus xanthus under conditions in which cells aggregate and form fruiting bodies. In liquid medium, glycerol- or dimethyl sulfoxide-induced sporulating cultures exhibited a sharp but transient rise in cyclic AMP concentration after 45 min.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1975

Regulation of development in Myxococcus xanthus: effect of 3':5'-cyclic AMP, ADP, and nutrition.

An assay was developed to study the regulation of fruiting in Myxococcus xanthus. The nucleotides, adenosine 3':5'-cyclic monophosphate (cyclic AMP) and adenosine diphosphate (ADP), were found to greatly stimulate fruiting under the assay conditions. Very sharp concentration optima were observed. Even under conditions of starvation, these nucleotides greatly increased the number of aggregation sites. Nutrition was found to influence fruiting body morphology. The effect of amino acids on the nucleotide stimulation of fruiting was studied under our assay conditions. L-Methionine and L-isoleucine (1 mM) completely blocked either L-threonine or D,L-diaminopimelic acid synergistically enhanced the amount of fruiting in the presence of these nucleotides. The data presented suggest the existence of differentiation-related regulatory compounds in M. xanthus.

Adenosine Diphosphate↗
PubMed1975

Thyroid-stimulating hormone regulation of ornithine decarboxylase activity in the thyroid.

TSH (1.0 U im) caused a 22-fold increase in thyroidal ornithine decarboxylase activity (ODC) 6 hours after administration in intact rats. Hypophysectomized rats treated with 1 U TSH showed a 5-fold increase in thyroid ODC activity. This stimulation appeared to be specific for TSH since hormones known to induce ODC activity in other target tissues, such as ACTH or LH, showed no significant stimulation. DIBUTYRYL CYCLIC AMP and aminopylline caused a 12-fold increase in ODC activity 5 hours after administration. Prostaglandins have also been implicated in the TSH-induced stimulation of cyclic AMP. Indomethacin (1.0 mg/100 g body wt, ip), an inhibitor of prostaglandin synthesis, was administered 3 hours before TSH with a resulting 30% diminution (P less than .001) in ODC activity compared with the administration of TSH alone. To rule out the possibility that the increase in ODC activity with TSH might be due to increased thyroid hormone secretion, ODC activity was evaluated 6 hours after triiodothyronine administration (60 mug/100 g body wt), and no significant increase in thyroid ODC activity was found. Stimulation of ODC activity was 90% inhibited by the intraperitoneal administration of actinomycin D (80 mug/100 g body wt) or cycloheximide (400 mug/100 g body wt) given simultaneously with TSH. These results indicated that TSH specifically stimulated thyroid ODC activity, which may be important for the growth-promoting action of the hormone on the thyroid gland. This action may be mediated by cAMP and prostaglandins and may require new protein synthesis.

Adrenocorticotropic Hormone↗
PubMed1974

Cell division in Escherichia coli: analysis of double mutants for filamentation and abnormal septation of deoxyribonucleic acid-less cells.

The link between chromosome termination, initiation of cell division, and choice of division sites was studied in Escherichia coli by preparing double mutants. Hybrid mutants containing div52-ts, a cell division initiation mutation, and min, mutations which affect the choice of division sites resulting in the septation of minicells, were characterized. The mutants produced minicells and normal cells coordinately under all conditions studied, although the fraction of minicells is half that of the parental minicell strain. The mutant gradually stopped dividing at both the median and minicell septation sites when transferred from 30 to 41 C in rich medium. A synchronous cell division of filaments was induced 15 min after addition of chloramphenicol to the medium, even at 41 C. Divisions were observed at both normal and minicell sites. These results indicate that div52-ts and min functions share a common step in a cell division pathway. A double mutant containing div52-ts and div27-ts, a dnaB mutant which divides in the absence of DNA synthesis, was characterized. The mutant continues to divide after a shift to the high temperature, although at a reduced rate. The behavior of this hybrid mutant suggests a hypothesis that the chromosome termination signal and div52-ts division initiation signal act on a single membrane site which is altered in div27-ts strains.

Cell Count↗
PubMed1973

Nucleoid condensation and cell division in Escherichia coli MX74T2 ts52 after inhibition of protein synthesis.

The reorganization of the bacterial nucleoid of an Escherichia coli mutant, MX74T2 ts52, was studied by electron microscopy after protein synthesis inhibition by using whole mounts of cell ghosts, ultrathin-sectioning, and freeze-etching. The bacterial nucleoid showed two morphological changes after chloramphenicol addition: deoxyribonucleic acid (DNA) localization and DNA condensation. DNA localization was observed 10 min after chloramphenicol addition; the DNA appeared as a compact, solid mass. DNA condensation was observed at 25 min; the nucleoid appeared as a cytoplasm-filled sphere, often opened at one end. Ribosomes were observed in the center. Giant nucleoids present in some mutant filaments showed fused, spherical nucleoids arranged linearly, suggesting that the tertiary structure of the nucleoid reflects the number of replicated genomes. Inhibitors which directly or indirectly blocked protein synthesis and caused DNA condensation were chloramphenicol, puromycin, amino acid starvation, rifampicin, or carbonyl cyanide m-chlorophenyl hydrazone. All inhibitors that caused cell division in the mutant also caused condensation, although some inhibitors caused condensation without cell division. Nucleoid condensation appears to be related to chromosome structure rather than to DNA segregation upon cell division.

Amino Acids↗