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Dive into the research topics where Robert R. Klevecz is active.

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Featured researches published by Robert R. Klevecz.


Experimental Cell Research | 2003

Generation and maintenance of synchrony in Saccharomyces cerevisiae continuous culture

Douglas B. Murray; Robert R. Klevecz; David Lloyd

Cultures of Saccharomyces cerevisiae grown continuously produce an autonomous oscillation in many metabolic outputs. The most conveniently measured variable, i.e., dissolved oxygen concentration, oscillates with a period of 40-55 min. Previously we have identified two compounds capable of resetting phase, acetaldehyde and hydrogen sulfide. The phase-response curves constructed for acetaldehyde show a strong (Type 0) response at 3.0 mM and a weak (Type 1) response at 1.0 mM. Ammonium sulfide phase-response curves (pulse injected at 1.0 microM and 3.0 microM) revealed that sulfide is only an effective perturbation agent when endogenous sulfide concentrations are at a maximum. Also only Type 1 phase responses were observed. When the phase-response curve for sulfite (at 3.0 M) was constructed, phase responses were at a maximum at 60 degrees, indicating the possible involvement of sulfite in cell synchronization. It is concluded that endogenously produced acetaldehyde and sulfite tune the oscillation of mitochondrial energization state whereas sulfide mediates population synchrony.


Cell | 1975

The temporal structure of S phase

Robert R. Klevecz; Beverly A. Keniston; Larry L. Deaven

DNA synthesis in the S phase of V79 and CHO Chinese hamster cells was examined in detail using an automated system for selection and subculturing of mitotic cells and four different assays for DNA synthesis. Flow microfluorometric (FMF) analysis showed that the selected populations were highly synchronous with few noncycling cells. In CHO cells changes in mean and modal fluorescence in the FMF suggested that DNA content increased in a saltatory fashion with 10-20% of the DNA replicated in early S, 40% in mid S, and 40-50% in late S. Pulse labeling and acid precipitation revealed a repeatable pattern of fluctuations in the rate of isotope incorporation with the maximum rate occurring late in S both V79 and CHO. Autoradiography proved to be the best means of accurately determining the beginning of S phase. Cumulative labeling from mitosis to points in S exaggerated the differences in rate between early and late S, so that significant DNA synthesis in early S might easily be overlooked using this method. In CHO cells DNA-specific fluorescence by the Kissane and Robins assay supported the isotopic incorporation data and the FMF analyses by exhibiting a stepwise increase. In V79 cells, S phase lasts only 5 or 5.5 hr, and consequently the mid S and late S steps in fluorescence are compressed. In V79, greater than 80% of the increase in DNA-specific fluorescence occurred between 4.5 and 7 hr after mitotic selection. In both cell lines, fluorescence in early S phase frequently increased transiently to maximum and then decreased.


Science | 1969

Temporal Coordination of DNA Replication with Enzyme Synthesis in Diploid and Heteroploid Cells

Robert R. Klevecz

The rate of DNA synthesis in the S phase of growth of synchronized diploid Chinese hamster cells shows two maximums, while in heteroploid hamster cells the DNA replication rate is constant. In diploid cells a reciprocal relationship exists between maximum DNA synthetic rates and maximum lactate dyhydrogenase and thymidine kinase enzyme levels. Enzyme activity in heteroploid cells increases continuously through the cell cycle with no evidence of oscillations. It seems possible that these differences in molecular organization may accompany or precede the transition to heteroploidy.


Gynecologic Oncology | 1987

Tumor DNA content as a prognostic feature in advanced epithelial ovarian carcinoma

Doron Blumenfeld; Patricia S. Braly; Jonathan Ben-Ezra; Robert R. Klevecz

Tumor DNA content (ploidy) was determined in 84 patients with epithelial ovarian carcinoma. Stage II-IV. A total of 251 DNA histograms generated by flow cytometry on cells derived from paraffin-embedded specimens were analyzed retrospectively. Of the 84 patients, 44 had tumors which were aneuploid, whereas 33 had diploid, and 7 had tetraploid tumors. Cox regression analysis revealed that age (P less than 0.001), stage (P less than 0.001), and ploidy (P less than 0.001) were independent prognostic features. The median survival time was 19 months and 48 months, respectively, in aneuploid and euploid tumors (P less than 0.001). The size of residual after surgery lost its significance when corrected for stage. Multivariate analysis in Stage III tumors revealed that ploidy was the most important prognostic factor (P less than 0.001) followed by age (P less than 0.025). A remarkable stability of cellular DNA content was found when the primary tumor was compared to the following groups: (1) various metastatic specimens from the primary operation in the same patient; (2) specimens analyzed sequentially from primary, secondary, and tertiary exploratory laparotomy; and (3) peritoneal washings before and after intraperitoneal chemotherapy.


Proceedings of the National Academy of Sciences of the United States of America | 2006

A rapid genome-scale response of the transcriptional oscillator to perturbation reveals a period-doubling path to phenotypic change

Caroline M. Li; Robert R. Klevecz

Perturbation of the gated-synchrony system in yeast with phenelzine, an antidepressant drug used in the treatment of affective disorders in humans, leads to a rapid lengthening in the period of the genome-wide transcriptional oscillation. The effect is a concerted, genome-scale change in expression that is first seen in genes maximally expressed in the late-reductive phase of the cycle, doubling the length of the reductive phase within two cycles after treatment. Clustering of genes based on their temporal patterns of expression yielded just three super clusters whose trajectories through time could then be mapped into a simple 3D figure. In contrast to transcripts in the late-reductive phase, most transcripts do not show transients in expression relative to others in their temporal cluster but change their period in a concerted fashion. Mapping the trajectories of the transcripts into low-dimensional surfaces that can be represented by simple systems of differential equations provides a readily testable model of the dynamic architecture of phenotype. In this system, period doubling may be a preferred pathway for phenotypic change. As a practical matter, low-amplitude, genome-wide oscillations, a ubiquitous but often unrecognized attribute of phenotype, could be a source of seemingly intractable biological noise in microarray studies.


Experimental Cell Research | 1978

Synthesis of poly(adenosine diphosphate ribose) in synchronized Chinese hamster cells.

Nathan A. Berger; Aaron S. Kaichi; Palmer G. Steward; Robert R. Klevecz; Gerald L. Forrest; Stephen D. Gross

Abstract Chinese hamster ovary cells were synchronized by mitotic selection and used to study the relation of poly(adenosine diphosphate ribose) synthesis to DNA synthesis and the different phases of the cell cycle. DNA synthesis was measured in cells rendered permeable to exogenously supplied nucleotides. Poly(ADPR) synthesis was also measured in permeable cells in the presence of both minimum and maximum DNA damage. The maximum DNA damage was produced by treating the cells with saturating concentrations of DNase. As anticipated, the DNA synthesis complex showed its maximum activity during S phase and showed 4–5-fold less activity during the other phases of the cell cycle. The basal level of poly(ADPR) synthesis was elevated during G1, fell to its lowest level during S phase, then increased during G2 and rose to its highest level during G1. The DNase responsive activity of poly(ADPR) synthesis was relatively constant thru the cell cycle but showed a peak at the end of S phase; then the activity decreased during the subsequent G2-M period.


Molecular Biology Reports | 2001

Genome wide oscillations in expression: Wavelet analysis of time series data from yeast expression arrays uncovers the dynamic architecture of phenotype

Robert R. Klevecz; Douglas B. Murray

A reanalysis of expression arrays in yeast cells synchronized by alpha factor blockade or through the use of temperature sensitive mutants uncovered a genome wide pattern of oscillations in mRNA concentrations. Using wavelet decomposition as a signal processing technique and enhancement strategies borrowed from image processing, noise and trends in the Stanford yeast cell cycle data were partitioned away from time series profiles to uncover genome-wide oscillations in expression. These oscillations which were typically of cell cycle or half cell cycle duration, 40 and 80 minutes in the Stanford data set suggest that there are large-scale temporal structures and high frequency oscillations in mRNA levels through the cell cycle. Wavelet decomposition, which acts like a band pass filter bank, was used to determine where most of the power appeared in the decomposition. The ∼40-min oscillation is mirrored in continuous chemostat cultures. In these cultures, metabolic synchrony involving an unknown proportion of the transcriptome can be monitored by measurement of oxygen consumption and can be sustained for weeks. These 40-min oscillations are stable and precise with coefficients of variation less than 1% for both period and amplitude. The hypothesis that high and low amplitude oscillations are a ubiquitous property of the genetic regulatory circuitry was supported by the observation of period doubling bifurcations in the distribution of population doubling times in yeast.


Experimental Cell Research | 1976

The cell cycle of low passage and high passage human diploid fibroblasts.

L.N. Kapp; Robert R. Klevecz

Abstract Using mitotic selection, synchronous populations of passage 25 and passage 50 WI38 cells were obtained. Thymidine incorporation, mitotic index, and labeling index were determined. No great differences could be seen in the organization of the cell cycle of low passage and high passage cells. Although labeling indices for passage 25 and passage 50 exponential cells were 83% and 37%, respectively, 75% of all mitotically selected cells were found to enter S phase, regardless of passage number. Thus, the loss of late passage diploid cell cultures does not occur from alteration of the cell cycle in the majority of rapidly proliferating cells.


Experimental Cell Research | 1982

Temperature compensation in the mammalian cell cycle

Robert R. Klevecz; Gary A. King

Abstract Random and synchronous V79 cells were shifted from 37.5 °C to temperatures between 29 ° and 41 °C. Intermitotic time determinations of random cultures showed an increase in generation time and a broadening in the distribution of generation times in cells whose cycle spanned the temperature shift, but only a slight increase in generation time after one generation at temperatures between 34 °–40 °C. At 33.5 °C and below there was a stepwise increase in generation time. When cells grown at non-standard temperatures were allowed to habituate for 48 h at the altered temperature prior to analysis, the increase in median intermitotic time was slightly less in comparison to analyses done after only one generation following the temperature step. The Q10 for cell division of cells growing at temperatures from 34 ° to 40 °C was between 1.15 and 1.26, suggesting that the mammalian cell cycle is temperature compensated over a limited (6–7 °C) temperature span. Mammalian cells in culture appear to have the same capacity for temperature compensation in their cell cycle as do unicellular eukaryotes. The fact that cycle time at lower temperatures increases in a discrete manner is taken as evidence for a quantal clock.


Biochimica et Biophysica Acta | 1974

Detecting small quantities of DNA on CsCl gradients

Leon N. Kapp; Sandra L. Brown; Robert R. Klevecz

Abstract The fluorescent assay of Kissane and Robbins can be applied to detect low levels of DNA in CsCl gradients and is capable of resolving buoyant density distribution patterns from gradients containing as little as 2–4 μg of DNA.

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James L. Bolen

City of Hope National Medical Center

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Gerald L. Forrest

City of Hope National Medical Center

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John A. Remington

City of Hope National Medical Center

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Leon N. Kapp

City of Hope National Medical Center

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Caroline M. Li

City of Hope National Medical Center

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Doron Blumenfeld

City of Hope National Medical Center

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Oscar Durán

City of Hope National Medical Center

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Stephen D. Gross

City of Hope National Medical Center

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