scholarly journals Liz1p, a Novel Fission Yeast Membrane Protein, Is Required for Normal Cell Division When Ribonucleotide Reductase Is Inhibited

1999 ◽  
Vol 10 (2) ◽  
pp. 245-257 ◽  
Author(s):  
Elizabeth B. Moynihan ◽  
Tamar Enoch
Keyword(s):  
Cell Cycle ◽  
Ribonucleotide Reductase ◽  
Cell Cycle Progression ◽  
Transmembrane Protein ◽  
Reductase Activity ◽  
Acid Protein ◽  
Affect Cell Cycle Progression ◽  
Transmembrane Transporters ◽  
Ribonucleotide Reductase Activity ◽  
Amino Acid Protein

Ribonucleotide reductase activity is required for generating deoxyribonucleotides for DNA replication. Schizosaccharomyces pombe cells lacking ribonucleotide reductase activity arrest during S phase of the cell cycle. In a screen for hydroxyurea-sensitive mutants in S. pombe, we have identified a gene,liz1 +, which when mutated reveals an additional, previously undescribed role for ribonucleotide reductase activity during mitosis. Inactivation of ribonucleotide reductase, by either hydroxyurea or a cdc22-M45 mutation, causesliz1 − cells in G2 to undergo an aberrant mitosis, resulting in chromosome missegregation and late mitotic arrest. liz1 + encodes a 514-amino acid protein with strong similarity to a family of transmembrane transporters, and localizes to the plasma membrane of the cell. These results reveal an unexpected G2/M function of ribonucleotide reductase and establish that defects in a transmembrane protein can affect cell cycle progression.

DNA precursor pools and ribonucleotide reductase activity: distribution between the nucleus and cytoplasm of mammalian cells

1985 ◽  
Vol 5 (12) ◽  
pp. 3443-3450
Author(s):  
J M Leeds ◽  
M B Slabaugh ◽  
C K Mathews
Keyword(s):  
Cell Cycle ◽  
Ribonucleotide Reductase ◽  
Cho Cells ◽  
Mammalian Cells ◽  
Plasma Membranes ◽  
Reductase Activity ◽  
Cell Activity ◽  
S Phase ◽  
Whole Cell ◽  
Ribonucleotide Reductase Activity

Nuclear and whole-cell deoxynucleoside triphosphate (dNTP) pools were measured in HeLa cells at different densities and throughout the cell cycle of synchronized CHO cells. Nuclei were prepared by brief detergent (Nonidet P-40) treatment of subconfluent monolayers, a procedure that solubilizes plasma membranes but leaves nuclei intact and attached to the plastic substratum. Electron microscopic examination of monolayers treated with Nonidet P-40 revealed protruding nuclei surrounded by cytoskeletal remnants. Control experiments showed that nuclear dNTP pool sizes were stable during the time required for isolation, suggesting that redistribution of nucleotides during the isolation procedure was minimal. Examination of HeLa whole-cell and nuclear dNTP levels revealed that the nuclear proportion of each dNTP was distinct and remained constant as cell density increased. In synchronized CHO cells, all four dNTP whole-cell pools increased during S phase, with the dCTP pool size increasing most dramatically. The nuclear dCTP pool did not increase as much as the whole-cell dCTP pool during S phase, lowering the relative nuclear dCTP pool. Although the whole-cell dNTP pools decreased after 30 h of isoleucine deprivation, nuclear pools did not decrease proportionately. In summary, nuclear dNTP pools in synchronized CHO cells maintained a relatively constant concentration throughout the cell cycle in the face of larger fluctuations in whole-cell dNTP pools. Ribonucleotide reductase activity was measured in CHO cells throughout the cell cycle, and although there was a 10-fold increase in whole-cell activity during S phase, we detected no reductase in nuclear preparations at any point in the cell cycle.

scholarly journals Cyclin E2, a Novel G1 Cyclin That Binds Cdk2 and Is Aberrantly Expressed in Human Cancers

1999 ◽  
Vol 19 (1) ◽  
pp. 612-622 ◽  
Author(s):  
Jean M. Gudas ◽  
Marc Payton ◽  
Sushil Thukral ◽  
Eddy Chen ◽  
Michael Bass ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Mammalian Cells ◽  
Cell Cycle Progression ◽  
Expressed Sequence Tag ◽  
Cyclin E ◽  
Cyclin E1 ◽  
Acid Protein ◽  
Cyclin E2 ◽  
Rate Limiting ◽  
Amino Acid Protein

ABSTRACT A novel cyclin gene was discovered by searching an expressed sequence tag database with a cyclin box profile. The human cyclin E2 gene encodes a 404-amino-acid protein that is most closely related to cyclin E. Cyclin E2 associates with Cdk2 in a functional kinase complex that is inhibited by both p27Kip1 and p21Cip1. The catalytic activity associated with cyclin E2 complexes is cell cycle regulated and peaks at the G1/S transition. Overexpression of cyclin E2 in mammalian cells accelerates G1, demonstrating that cyclin E2 may be rate limiting for G1 progression. Unlike cyclin E1, which is expressed in most proliferating normal and tumor cells, cyclin E2 levels were low to undetectable in nontransformed cells and increased significantly in tumor-derived cells. The discovery of a novel second cyclin E family member suggests that multiple unique cyclin E-CDK complexes regulate cell cycle progression.

Activities of both ribonucleotide reductase subunits, M1 and M2, decrease upon serum starvation of baby hamster kidney 21/C13 cells

1987 ◽  
Vol 65 (1) ◽  
pp. 35-42 ◽  
Author(s):  
Eric A. Cohen ◽  
Mario Filion ◽  
Martha Suh ◽  
Yves Langelier
Keyword(s):  
Cell Cycle ◽  
Molecular Weight ◽  
Ribonucleotide Reductase ◽  
Protein Level ◽  
Mammalian Cells ◽  
Reductase Activity ◽  
Serum Starvation ◽  
Baby Hamster Kidney ◽  
M1 Protein ◽  
Ribonucleotide Reductase Activity

Ribonucleotide reductase from mammalian cells is composed of two nonidentical subunits M1 and M2 which are both required to form the catalytic site. The level of ribonucleotide reductase activity is cell cycle controlled and several reports suggest that this control is achieved mainly by the regulation of M2 subunit synthesis. In the present study, we have found that the activities of both subunits decreased markedly upon serum starvation in the Syrian baby hamster kidney 21/C13 cell line. These decreases did not seem to be correlated with the appearance of an inhibitory factor in serum-starved cells. Quantification of the amount of the M1 subunit protein (89 000 molecular weight) by [12P]dTTP photoaffinity labelling revealed that the decrease in M1 activity was not due to variation in M1 protein level. Therefore, a posttranslational mechanism probably exists which inactivates M1 subunit when cells stay in the quiescent (G0) state and this mechanism could play an important role in the control of ribonucleotide reductase activity.

scholarly journals DNA precursor pools and ribonucleotide reductase activity: distribution between the nucleus and cytoplasm of mammalian cells.

1985 ◽  
Vol 5 (12) ◽  
pp. 3443-3450 ◽  
Author(s):  
J M Leeds ◽  
M B Slabaugh ◽  
C K Mathews
Keyword(s):  
Cell Cycle ◽  
Ribonucleotide Reductase ◽  
Cho Cells ◽  
Mammalian Cells ◽  
Plasma Membranes ◽  
Reductase Activity ◽  
Cell Activity ◽  
S Phase ◽  
Whole Cell ◽  
Ribonucleotide Reductase Activity

Nuclear and whole-cell deoxynucleoside triphosphate (dNTP) pools were measured in HeLa cells at different densities and throughout the cell cycle of synchronized CHO cells. Nuclei were prepared by brief detergent (Nonidet P-40) treatment of subconfluent monolayers, a procedure that solubilizes plasma membranes but leaves nuclei intact and attached to the plastic substratum. Electron microscopic examination of monolayers treated with Nonidet P-40 revealed protruding nuclei surrounded by cytoskeletal remnants. Control experiments showed that nuclear dNTP pool sizes were stable during the time required for isolation, suggesting that redistribution of nucleotides during the isolation procedure was minimal. Examination of HeLa whole-cell and nuclear dNTP levels revealed that the nuclear proportion of each dNTP was distinct and remained constant as cell density increased. In synchronized CHO cells, all four dNTP whole-cell pools increased during S phase, with the dCTP pool size increasing most dramatically. The nuclear dCTP pool did not increase as much as the whole-cell dCTP pool during S phase, lowering the relative nuclear dCTP pool. Although the whole-cell dNTP pools decreased after 30 h of isoleucine deprivation, nuclear pools did not decrease proportionately. In summary, nuclear dNTP pools in synchronized CHO cells maintained a relatively constant concentration throughout the cell cycle in the face of larger fluctuations in whole-cell dNTP pools. Ribonucleotide reductase activity was measured in CHO cells throughout the cell cycle, and although there was a 10-fold increase in whole-cell activity during S phase, we detected no reductase in nuclear preparations at any point in the cell cycle.

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