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Biomedical subjects

A Oppenheim

Publications and source records attributed to A Oppenheim.

At least 91 records · Page 5Linked to original sources
PubMed1984

DNA methylation pattern is determined by the intracellular level of the methylase.

Extrachromosomal plasmid DNA is transiently undermethylated in Escherichia coli during amplification in the presence of chloramphenicol. In addition, undermethylation of phage lambda DNA was observed after thermal induction of a lambda c1857 lysogen while the integrated lambda phage DNA was found to be fully methylated. These methylation pattern changes occur under conditions (extensive replication) in which the intracellular methylase level becomes limiting. In an E. coli strain that harbors a plasmid that carries the dam methylase gene and therefore overproduces dam methylase, there is no undermethylation of dam sites in either of the extrachromosomal DNAs. The sites that are methylated by the mec methylase in both plasmid and lambda phage DNAs were undermethylated in the dam overproducer as well. These results indicate that the intracellular level of the E. coli methylase determines the DNA methylation pattern.

Bacteriophage lambda↗
PubMed1984

Marked hypotonic polyuria resulting from nephrogenic diabetes insipidus with partial sensitivity to vasopressin.

We studied two women with severe hypotonic polyuria whose symptoms dated from infancy. We eliminated the possibility of central diabetes insipidus (DI) and primary polydipsia, and established the presence of nephrogenic DI on the basis of: 1) the interrelationships between plasma osmolality, urine osmolality, and urinary AVP; and 2) impaired antidiuretic responses to AVP and 1 deamino-8-D-arginine vasopressin. Though 25-50 times as resistant to 1 deamino-8-D-arginine vasopressin nasal spray as patients with central DI, these patients could be treated effectively with large doses of the nasal spray. One patient has been so treated for more than a year with dramatic improvement in her polydipsia, polyuria, and sense of well-being.

Administration, Intranasal↗
PubMed1983

Anaplastic thyroid cancer presenting with hyperthyroidism.

Primary thyroid malignancies typically do not interfere with thyroid function. A patient is reported with anaplastic thyroid carcinoma presenting with hyperthyroidism; this is believed to be the first such case described. Prior to the onset of the thyroidal process, the patient was clinically euthyroid. It is concluded that the mechanism of thyrotoxicosis is analogous to that of subacute thyroiditis: rapid tissue necrosis with resultant release of thyroid hormone.

Carcinoma↗
PubMed1981

Separation of closed circular DNA from linear DNA by electrophoresis in two dimensions in agarose gels.

A method that provides an easy, rapid, and reproducible way for separating closed circular DNA species from linear DNA and nicked circles is described. The method is based on the difference in mobility of form I (supercoiled) DNA and form II (nicked circles), and the differential mobility of relaxed circular DNA in the presence and absence of ethidium bromide (EtdBr). It can be used for detection or for purification of plasmid, episomal, or viral DNA from the bulk of cellular DNA, or from other DNA mixtures.

Bacteriophage lambda↗
PubMed1981

Initiation points for cellular deoxyribonucleic acid replication in human lymphoid cells converted by Epstein-Barr virus.

Replicon size was estimated in two Epstein-Barr virus (EBV)-negative human lymphoma lines, BJAB and Ramos, and four EBV-positive lines derived from the former ones by infection (conversion) with two viral strains, B95-8 and P3HR-1. Logarithmic cultures were pulse-labeled with [3H]thymidine, and the deoxyribonucleic acid was spread on microscopic slides and autoradiographed by the method of Huberman and Riggs. After developing, replication forks were visualized as silver grain tracks on the autoradiograms. Average replicon size was estimated by scoring the number of replication forks per constant length of deoxyribonucleic acid and by measuring distances between centers of adjacent tracks, followed by detailed statistical analyses. Three of the four EBV-converted cell lines, BJAB/B95-8, Ra/B95-8, and Ra/HRIK, were found to have significantly shorter replicons (41, 21, 54% shorter, respectively), i.e., more initiation points, than their EBV-negative parents. BJAB/HRIK had replicons which were only slightly shorter (11%) than those of BJAB. However, analysis of track length demonstrated that extensive track fusion occurred during the labeling of BJAB/ HRIK, implying that its true average replicon size is shorter than the observed value. The results indicate that in analogy to simian virus 40, EBV activates new initiation points for cellular DNA replication in EBV-transformed cells.

Autoradiography↗
PubMed1981

No activation of new initiation points for deoxyribonucleic acid replication in BALB/c 3T3 cells transformed by Kirsten sarcoma virus.

BALB/c 3T3 cells were transformed by Kirsten sarcoma virus, and five clones were isolated in soft agar. Average replicon sizes of the transformed cell lines were estimated by the method of fiber-autoradiography (J. A. Huberman and A. D. Riggs, J. Mol. Biol.32:327-341, 1968) and found to be the same size as the nontransformed 3T3 cells, analyzed in parallel. The results indicate that, unlike simian virus 40 and Epstein-Barr virus, Kirsten sarcoma virus does not activate new initiation points for cellular deoxyribonucleic acid replication in murine sarcoma virus-transformed BALB/c 3T3 cells.

3T3 Cells↗
PubMed1978

Regulation of the int gene of bacteriophage lambda: activation by the cII and cIII gene products and the role of the Pi and Pl promoters.

The activation of the int gene by the cII and cIII gene products was studied by analysing int expression following infection of UV-irradiated cells by various phage mutants. Residual expression of int, probably from Pl, takes place in the absence of cII/cIII activation. Activation of the int gene, like that of the cI repressor gene, is poor at low multiplicities of infection. The mutation intC, which allows constitutive int expression in the lysogenic state, partially relieves the requirement for cII and cIII activation. The kinetics of Int synthesis after addition of the inhibitor rifampicin suggest that the activation occurs at the transcriptional level.

Coliphages↗
PubMed1977

Repressor and int synthesis of bacteriophage lambda in the E. coli host mutant ER437.

Analysis of lambda phage infection of the host mutant ER437 by SDS polyacrylamide gel electrophoresis and autoradiography has revealed altered expression of repressor and integration function (Int). We show that in this host Int as well as repressor synthesis is not dependent upon the lambdacIII gene product in the usual manner, nor is their synthesis turned off in the normal way.

Autoradiography↗
PubMed1977

Initiation points for DNA replication in nontransformed and simian virus 40-transformed Chinese hamster lung cells.

Randomly growing Chinese hamster lung cells were pulse-labeled with 3H-thymidine, and the replicating forks of individual DNA fibers were visualized by autoradiography. When grown in complete medium, wild-type SV40-transformed cells had more forks per unit length of DNA than nontransformed cells. In isoleucine-depleted medium, wild-type SV40-transformed cells had fewer forks per unit length than those few nontransformed cells (1-3% of the population) which continued DNA replication. Cells transformed by a tsA mutant of SV40 when grown at the permissive temperature had more forks per unit length in complete medium and fewer forks per unit length in depleted medium than nontransformed cells, but when grown at the restrictive temperature, the tsA-transformed cells behaved like nontransformed cells.

Animals↗