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Biomedical subjects

T Weinert

Publications and source records attributed to T Weinert.

At least 19 recordsLinked to original sources
PubMed2000

Closing the gaps among a web of DNA repair disorders.

As recently as six years ago, three human diseases with similar phenotypes were mistakenly believed to be caused by a single genetic defect. The three diseases, Ataxia-telangiectasia, Nijmegen breakage syndrome, and an AT-like disorder are now known, however, to have defects in three separate genes: ATM, NBS1, and MRE11. Furthermore, new recent studies have shown now that all three gene products interact; the ATM kinase phosphorylates NBS1, which, in turn, associates with MRE11 to regulate DNA repair. Remarkably or expectedly, depending on one's point of view, the similarity in disease phenotypes is evidently due to defects in a common DNA repair pathway.

Ataxia Telangiectasia Mutated Proteins↗
PubMed1999

RAD53, DUN1 and PDS1 define two parallel G2/M checkpoint pathways in budding yeast.

Eukaryotic checkpoint genes regulate multiple cellular responses to DNA damage. In this report, we examine the roles of budding yeast genes involved in G2/M arrest and tolerance to UV exposure. A current model posits three gene classes: those encoding proteins acting on damaged DNA (e.g. RAD9 and RAD24), those transducing a signal (MEC1, RAD53 and DUN1) or those participating more directly in arrest (PDS1). Here, we define important features of the pathways subserved by those genes. MEC1, which we find is required for both establishment and maintenance of G2/M arrest, mediates this arrest through two parallel pathways. One pathway requires RAD53 and DUN1 (the 'RAD53 pathway'); the other pathway requires PDS1. Each pathway independently contributes approximately 50% to G2/M arrest, effects demonstrable after cdc13-induced damage or a double-stranded break inflicted by the HO endonuclease. Similarly, both pathways contribute independently to tolerance of UV irradiation. How the parallel pathways might interact ultimately to achieve arrest is not yet understood, but we do provide evidence that neither the RAD53 nor the PDS1 pathway appears to maintain arrest by inhibiting adaptation. Instead, we think it likely that both pathways contribute to establishing and maintaining arrest.

Alleles↗
PubMed1999

Saccharomyces cerevisiae checkpoint genes MEC1, RAD17 and RAD24 are required for normal meiotic recombination partner choice.

Checkpoint gene function prevents meiotic progression when recombination is blocked by mutations in the recA homologue DMC1. Bypass of dmc1 arrest by mutation of the DNA damage checkpoint genes MEC1, RAD17, or RAD24 results in a dramatic loss of spore viability, suggesting that these genes play an important role in monitoring the progression of recombination. We show here that the role of mitotic checkpoint genes in meiosis is not limited to maintaining arrest in abnormal meioses; mec1-1, rad24, and rad17 single mutants have additional meiotic defects. All three mutants display Zip1 polycomplexes in two- to threefold more nuclei than observed in wild-type controls, suggesting that synapsis may be aberrant. Additionally, all three mutants exhibit elevated levels of ectopic recombination in a novel physical assay. rad17 mutants also alter the fraction of recombination events that are accompanied by an exchange of flanking markers. Crossovers are associated with up to 90% of recombination events for one pair of alleles in rad17, as compared with 65% in wild type. Meiotic progression is not required to allow ectopic recombination in rad17 mutants, as it still occurs at elevated levels in ndt80 mutants that arrest in prophase regardless of checkpoint signaling. These observations support the suggestion that MEC1, RAD17, and RAD24, in addition to their proposed monitoring function, act to promote normal meiotic recombination.

Cell Cycle Proteins↗
PubMed1998

DNA damage checkpoints update: getting molecular.

Eukaryotic checkpoint controls impose delays in the cell cycle in response to DNA damage or defects in DNA replication. Genetic and physiological studies in budding yeast have identified key genes and defined genetic pathways involved in checkpoint-mediated responses. Recent studies now lead to biochemical models that explain at least in part the arrest in G1 and delays during DNA replication after damage. Though progress in checkpoint controls has indeed been rapid, several observations identify puzzling aspects of checkpoint controls with few plausible explanations.

Animals↗
PubMed1997

G2/M checkpoint genes of Saccharomyces cerevisiae: further evidence for roles in DNA replication and/or repair.

We have cloned, sequenced and disrupted the checkpoint genes RAD17, RAD24 and MEC3 of Saccharomyces cerevisiae. Mec3p shows no strong similarity to other proteins currently in the database. Rad17p is similar to Rec1 from Ustilago maydis, a 3' to 5' DNA exonuclease/checkpoint protein, and the checkpoint protein Rad1p from Schizosaccharomyces pombe (as we previously reported). Rad24p shows sequence similarity to replication factor C (RFC) subunits, and the S. pombe Rad17p checkpoint protein, suggesting it has a role in DNA replication and/or repair. This hypothesis is supported by our genetic experiments which show that overexpression of RAD24 strongly reduces the growth rate of yeast strains that are defective in the DNA replication/repair proteins Rfc1p (cdc44), DNA pol alpha (cdc17) and DNA pol delta (cdc2) but has much weaker effects on cdc6, cdc9, cdc15 and CDC4 strains. The idea that RAD24 overexpression induces DNA damage, perhaps by interfering with replication/repair complexes, is further supported by our observation that RAD24 overexpression increases mitotic chromosome recombination in CDC4 strains. Although RAD17, RAD24 and MEC3 are not required for cell cycle arrest when S phase is inhibited by hydroxyurea (HU), they do contribute to the viability of yeast cells grown in the presence of HU, possibly because they are required for the repair of HU-induced DNA damage. In addition, all three are required for the rapid death of cdc13 rad9 mutants. All our data are consistent with models in which RAD17, RAD24 and MEC3 are coordinately required for the activity of one or more DNA repair pathways that link DNA damage to cell cycle arrest.

Alkylating Agents↗
PubMed1997

Yeast checkpoint controls and relevance to cancer.

Checkpoint controls arrest cells with defects in DNA replication or DNA damage. For several reasons, checkpoint controls may be relevant to ontogeny and treatment of cancer. Firstly, mutations in two human genes, TP53 and ATM, give rise to cellular defects in cell cycle checkpoints and are associated with cancer. Secondly, although checkpoint defects potentially render the cell damage sensitive, they may do so only in combination with other defects in the cell's response to damage. Therefore, manipulation of checkpoint defects, requiring a description of normal and mutant pathways, will be required for this type of therapeutic approach. Those pathways are being described in yeast cells. In budding yeast, the study of checkpoint genes has led to the view that these genes have many roles in the cellular responses to DNA damage, including roles in arrest in multiple stages of cell cycle, in transcriptional induction of repair genes, in DNA repair itself and additionally some undefined role in DNA replication. The checkpoint pathways and proteins that carry out these responses may consist of sensor proteins that detect damage, signaller proteins that transduce an inhibitory signal and target proteins that are altered to arrest cell division (or cause other changes in cell behaviour). Yeast genes that may act at each step have been identified, leading to a working model of checkpoint pathways. An initial step in the pathway may involve the processing of damage to an intermediate that signals arrest and acts in DNA repair. Human checkpoint pathways may have defects in processing damage as well.

Animals↗
PubMed1996

A meiotic recombination checkpoint controlled by mitotic checkpoint genes.

In budding yeast, meiotic recombination occurs at about 200 sites per cell and involves DNA double-strand break (DSB) intermediates. Here we provide evidence that a checkpoint control requiring the mitotic DNA-damage checkpoint genes RAD17, RAD24 and MEC1 ensures that meiotic recombination is complete before the first meiotic division (MI). First, RAD17, RAD24 and MEC1 are required for the meiotic arrest caused by blocking the repair of DSBs with a mutation in the recA homologue DMC1. Second, mec1 and rad24 single mutants (DMC1+) appear to undergo MI before all recombination events are complete. Curiously, the mitosis-specific checkpoint gene RAD9 is not required for meiotic arrest of dmc1 mutants. This shows that although mitotic and meiotic control mechanisms are related, they differ significantly. Rad17 and Rad24 proteins may contribute directly to formation of an arrest signal by association with single-strand DNA in mitosis and meiosis.

Cell Cycle Proteins↗
PubMed1995

Yeast checkpoint genes in DNA damage processing: implications for repair and arrest.

Yeast checkpoint control genes were found to affect processing of DNA damage as well as cell cycle arrest. An assay that measures DNA damage processing in vivo showed that the checkpoint genes RAD17, RAD24, and MEC3 activated an exonuclease that degrades DNA. The degradation is probably a direct consequence of checkpoint protein function, because RAD17 encodes a putative 3'-5' DNA exonuclease. Another checkpoint gene, RAD9, had a different role: It inhibited the degradation by RAD17, RAD24, and MEC3. A model of how processing of DNA damage may be linked to both DNA repair and cell cycle arrest is proposed.

Amino Acid Sequence↗
PubMed1993

Cell cycle checkpoints, genetic instability and cancer.

During the cell cycle, the order of events is maintained by controls termed checkpoints. Two checkpoints are sensitive to DNA damage, one that acts before mitosis and a second that acts before DNA replication. This is relevant to cancer because checkpoint mutants show genetic instability, and such instability is characteristic of many cancers. Studies of checkpoints in normal and cancer cells suggest a mechanistic relationship to the central cell cycle control p34CDC2 and its regulators. We suggest how mutations in these genes and those with a role in DNA metabolism may affect the function of checkpoints. A further link between checkpoints and cancer may be the p53 protein, which appears to function at the G1-S checkpoint. Consideration of checkpoints may provide more effective means for cancer treatment.

Animals↗
PubMed1989

Control of G2 delay by the rad9 gene of Saccharomyces cerevisiae.

In response to DNA damage, Saccharomyces cerevisiae cells arrest the cell cycle in the G2 phase. Arrest is defective in rad9 mutants; rad9 cells divide and die without repairing the damage. Several cell cycle mutants that are defective in DNA replication arrest in G2 at the restrictive temperature; this arrest is due to the RAD9 control function. Thus RAD9 is responsible for the fact that mitosis is normally dependent upon DNA replication, a function we term a 'checkpoint'. Four additional genes have been identified that are also components of the RAD9 checkpoint.

DNA Damage↗