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Biomedical subjects

A B Pardee

Publications and source records attributed to A B Pardee.

At least 217 records · Page 12Linked to original sources
PubMed1978

2-amino-isobutyric acid and 3-O-methyl-D-glucose transport in 3T3, SV 40-transformed 3T3 and revertant cell lines.

In order to further investigate the connection between transport and growth control, 3T3 cells, SV40 transformed 3T3 cells (SV101), and three revertant cell lines derived from SV101 which have regained certain manifestations of growth control were used. Transport rates of 2-amino-isobutyric acid and 3-O-methyl-D-glucose were measured in sparse, confluent, serum-starved, and serum-stimulated cultures. As shown before, cessation of 3T3 cell growth in G0 under conditions of confluence or serum deprivation was associated with reduced rates of transport for both compounds, whereas the density and serum dependence of growth and transport was largely eliminated in SV101. The density revertant F1SV101, which has regained density regulation of growth similar to 3T3 cells, has also regained density regulation of transport. Neither growth nor transport were serum dependent. The serum revertants AgammaSV7 and LsSV6 have regained both density and serum regulation of growth, but not according to the original mechanism of 3T3 cells of entry into a Go state. Transport was high under conditions of confluence or serum deprivation. Thus for these cells rates of transport were not reduced simply as a consequences of slower cell growth nor were low transport rates responsible for growth arrest. The data are consistent with the possibility that growth arrest specifically in the G0 state could shut off a number of cellular activities, including transport.

Aminoisobutyric Acids↗
PubMed1978

Control of DNA synthesis in tissue culture cells.

Eukaryotic DNA is functionally divided into thousands of replicons, each of which may be duplicated at a characteristic time within the DNA synthetic (S) period. Our approach toward an understanding of the molecular mechanisms which control orderly eukaryotic DNA synthesis has been: (a) to devise a method of cell synchrony in a suitable tissue culture system wherein all cells in the population enter and traverse the S period with a high degree of synchrony; (b) to determine, utilizing this system, precisely when during the S period critical events and macromolecular syntheses occur; and (c) to examine, by polyacrylamide-gel electrophoresis, the spectrum of proteins which become associated with chromatin during the S period in such a way as to suggest their involvement with DNA synthesis. Possible mechanisms for control are discussed based on the results presented here.

Cell Cycle↗
PubMed1978

Animal cells reversibly permeable to small molecules.

A cell preparation, useful for studying the regulation of metabolism, was developed by making monolayer baby hamster kidney cells permeable. Hypertonically treated cells were permeable to nucleotides, but retained their gross cellular morphology, intact organelles, 100% of their DNA, and 91% of their total protein. The permeable cell synthesized DNA, RNA, and protein rapidly when supplied with the appropriate substrates and cofactors. They either could remain permeable or were able to "reseal" when replaced in complete medium under appropriate conditions. Optimal conditions for DNA synthesis were established for permeable cells, giving rates equal to those of intact cells. Replication rather than repair was shown by the cell-cycle dependence of DNA synthesis and its discontinuous nature. Ribonucleotide reductase was active in permeable cells, permitting equal rates of DNA synthesis when ribonucleotide diphosphates or deoxyribonucleotide triphosphates were provided. Hydroxyurea did not inhibit DNA synthesis in permeable cells supplied with deoxyribonucleotide di- or triphosphates, but drastically inhibited DNA synthesis when ribonucleotide diphosphates were supplied. Hydroxyurea is therefore primarily an inhibitor of ribonucleotide reductase. Permeability was reversed, exposing permeable cells to [(3)H]thymidine triphosphate, which was incorporated, which labeled nuclei of cells that went on to mitosis. The reversible permeability procedure should prove especially useful in studying the functions of poorly penetrating compounds, such as drugs. Intact cells were unaffected by cytosine arabinoside triphosphate, while cells that had been made permeable and resealed were killed.

Cell Cycle↗
PubMed1978

Inhibition of Escherichia coli division by protein X.

We propose that protein X provides the connection between damage to Escherichia coli DNA and inhibition of septation and cell division. This connection is needed to guarantee that each new bacterium receives a complete DNA copy. We present several new experiments here which demonstrate that the degree to which septation is inhibited following damage to DNA is correlated with the amount of protein X that is produced. Rifampin selectively blocks protein X production. This drug was shown to allow cells whose DNA had been damaged by nalidixic acid to resume septation. Several mutants formed septa-less filaments and also produced protein X at 42 degrees C; rifampin both inhibited their production of protein X and permitted them to form septa and divide. Essentially complementary results were obtained with a dnaA mutant which at 42 degrees C stopped making DNA, did not produce protein X, and continued to divide; added bleomycin degraded DNA, induced protein X, and inhibited septation. These results, as well as previous observations, are all consistent with the proposal that protein X is produced as a consequence of DNA damage and is an inhibitor of septation. We suggest that septation could require binding of a single-stranded region of DNA to a septum site in the membrane. Protein X could block this binding by combining with the DNA. This control could provide an emergency mechanism in addition to the usually proposed coordination in which completion of DNA synthesis creates a positive effector for a terminal step of septation. Or it could be the sole coordinating mechanism, even under unperturbed growth conditions.

Bacterial Proteins↗
PubMed1975

Selective killing of transformed baby hamster kidney (BHK) cells.

We report here that certain drugs can protect Syrian baby hamster kidney cells (BHK) in culture against the lethal agents cytosine arabinonucleoside, hydroxyurea, and colcemid. Polyoma virus-transformed BHK cells (PyBHK) are killed under the same conditions. The protective drugs include caffeine and streptovitacin A. Kinetic studies show that these drugs act specifically in G1, and that they shift BHK cells from G1 into the G0 state at the restriction point, similar to the effects of high cell density or serum deprivation. These drugs do not block the growth of PyBHK cells nearly as effectively, consistent with a reduced effectiveness of restriction point control in virus-transformed cells. Consequently, the transformed cells around their cycle and are killed by the cell cycle phase-specific toxic agents, in contrast to the arrested BHK cells. These findings provide a model for studies on differential killing of tumor versus normal cells in vivo.

Antibiotics, Antineoplastic↗
PubMed1975

Cell cycle studies of mononucleate and cytochalasin-B--nduced binucleate fibroblasts.

The progress of mononucleate and cytochalasin-B-induced binucleate cells through the G1 period of the growth cycle has been studied. DNA synthesis was initiated in synchrony in both of the nuclei of cells rendered binucleate by a brief pulse of cytochalasin B. Furthermore, populations of these cells traversed the G1 period significantly faster than their mononucleate counterparts. That this effect was due to the presence of two nuclei in a common cytoplasm and not to the increased size of binucleate cells was suggested by studies of cells with altered nucleocytoplasmic ratios. No correlation was observed between protein content per cell and the rate of progress through G1. Evidence for the existence of nuclear-nuclear cooperation that results in a shortening of the G1 period is discussed.

Animals↗
PubMed1975

Model for regulation of Escherichia coli DNA repair functions.

A feedback loop for the regulation of the rec/lex-mediated DNA repair system is proposed. This model was formulated from experiments on the genetic and metabolic regulation of the rate of synthesis of protein X performed in this laboratory, and from genetic data obtained in other laboratories. Protein X is proposed to prevent DNA degradation by the recBC-coded exonuclease. The model states tht: (1) The lex (or exrA in E. coli B) gene codes for a repressor. (2) This repressor binds to an operator region of DNA consisting of the tif-zab region at 51 minutes on the E. coli chromosome. (3) The operator region controls the production of several proteins involved in DNA repair, including protein X. (4) The recA gene product is required to remove the lex-coded repressor from the operator. Thre recA gene could code for an antirepressor (inducer protein or a protease) or a modifer of recBC nuclease action; (5) Low molecular weight products of DNA degradation are effectors that activate the system. (6) Protein X limits recBC nuclease action by binding to single-stranded DNA.

Autoradiography↗
PubMed1975

Inhibition of an early event in the cell division cycle of Escherichia coli by FL1060, an amidinopenicillanic acid.

Analysis of exponential and synchronous cultures of Escherichia coli B/r after the addition of FL1060 indicates a block point for division by this agent some 15 to 20 min before the end of the preceding cell division cycle, a time corresponding to the beginning of the C period of the cell division cycle. Morphological examination of FL1060-treated synchronous cultures of E. coli /r was consistent with inhibition by FL1060 of a very early event in the cell division cycle. This event appears to be essential for normal cell surface elongation in a rod configuration. Temporary treatment of synchronous cultures of E. coli B/r with FL1060 resulted in division delay, the extent of which was a function of the duration of exposure to FL1060. However, even after relatively long times of FL1060 treatment the delayed divisions were still synchronous. Although FL1060 had no direct effect on deoxyribonucleic acid (DNA) synthesis, the synchronous delayed division occuring after temporary treatment with FL1060 were accompanied by a delay in the attainment of resistance of cell division to inhibitors of DNA, ribonucleic acid, and protein synthesis. These results suggest aht an FL1060-sensitive event initiates at the beginning of the C period of the cell division cycle of E. coli and is responsible for normal cell elongation. This cell elongation pathway procedes independently of DNA synthesis, but there is an interaction between this pathway and termination of a round of DNA replication in which a normal rod configuration is necessary to allow a signal for cell division to be generated upon completion of DNA replication.

Cell Division↗