Biomedical subjects

M Muzi Falconi

Publications and source records attributed to M Muzi Falconi.

8 recordsLinked to original sources

PubMed2000

DNA damage checkpoints and DNA replication controls in Saccharomyces cerevisiae.

In response to genotoxic agents and cell cycle blocks all eukaryotic cells activate a set of surveillance mechanims called checkpoints. A subset of these mechanisms is represented by the DNA damage checkpoint, which is triggered by DNA lesions. The activation of this signal transduction pathway leads to a delay of cell cycle progression to prevent replication and segregation of damaged DNA molecules, and to induce transcription of several DNA repair genes. The yeast Saccharomyces cerevisiae has been invaluable in genetically dissecting the DNA damage checkpoint pathway and recent findings have provided new insights into the architecture of checkpoint protein complexes, in their order of function and in the mechanisms controlling DNA replication in response to DNA damage.

Cell Cycle↗

PubMed1996

cdc18+ regulates initiation of DNA replication in Schizosaccharomyces pombe.

In the fission yeast Schizosaccharomyces pombe the cdc18'+gene is required both for initiation of DNA replication and for coupling mitosis to the completion of S phase. Cells lacking Cdc18 fail to enter S phase but still undergo nuclear division. Expression of cdc18+ is sufficient to drive a G1-arrested cdc10ts mutant into the S phase of the cell cycle, indicating that cdc18+ represents a critical link between passage through START and the initiation of DNA replication. Here we show that Cdcl8 is a highly unstable protein that is expressed only once per cell cycle at the boundary between GI and S phase. De novo synthesis of Cdc18 is required before, but not after, the initiation of DNA replication, indicating that Cdc18 function is not necessary once the initiation event has occurred. Overproduction of the protein results in an accumulation of cells with DNA content of greater than 2C and delays mitosis, suggesting that Cdc18 is sufficient to cause reinitiation of DNA replication within a given cell cycle. Our data indicate that the synthesis of Cdc18 protein is a critical rate-limiting step in the initiation of DNA replication during each cell cycle. The extreme lability of the protein may contribute to the prevention of reinitiation.

Cell Cycle↗

PubMed1993

De novo synthesis of budding yeast DNA polymerase alpha and POL1 transcription at the G1/S boundary are not required for entrance into S phase.

The POL1 gene, encoding DNA polymerase alpha (pol alpha) in Saccharomyces cerevisiae, is transiently transcribed during the cell cycle at the G1/S phase boundary. Here we show that yeast pol alpha is present at every stage of the cell cycle, and its level only slightly increases following the peak of POL1 transcription. POL1 mRNA synthesis driven by a GAL1 promoter can be completely abolished without affecting the growth rate of logarithmically growing yeast cultures for several cell divisions, although the amount of the pol alpha polypeptide drops below the physiological level. Moreover, alpha-factor-arrested cells can enter S phase and divide synchronously even if POL1 transcription is abolished. These results indicate that the level of yeast pol alpha is not rate limiting and de novo synthesis of the enzyme is not required for entrance into S phase.

Cell Cycle↗

PubMed1992

Overproduction and functional analysis of DNA primase subunits from yeast and mouse.

Eukaryotic DNA primases are composed of two distinct subunits of 48-50 and 58-60 kDa. The amino acid sequences derived from the nucleotide sequences of the cloned genes are known only for the yeast and mouse polypeptides, and the extensive homology between the corresponding mouse and yeast subunits suggests conservation of functional domains. We were able to express in Saccharomyces cerevisiae the homologous and mouse primase-encoding genes under the control of both the constitutive ADH1 and the inducible GAL1 strong promoters, thus obtaining strains producing relevant amounts of the different polypeptides. In vivo complementation studies showed that neither one of the wild-type mouse primase-encoding genes was able to rescue the lethal or temperature-sensitive phenotype caused by mutations in the yeast PRI1 or PRI2 genes, indicating that these proteins, even if structurally and functionally very similar, might be involved in critical species-specific interactions during DNA replication.

Animals↗

PubMed1992

Nucleotide sequence of 9.2 kb left of CRY1 on yeast chromosome III from strain AB972: evidence for a Ty insertion and functional analysis of open reading frame YCR28.

We report the 9210 bp sequence from a segment of yeast chromosome III cloned from strain AB972 in lambda PM3270. Analysis of this sequence and its comparison with the one derived from the corresponding segment of strain XJ24-24A revealed that the AB972 region contains a duplication of about 2 kb and a Ty element, which are not found in XJ24-24A and cause a quite significant rearrangement of the whole region. We performed functional analysis of YCR28, the largest open reading frame we found in both AB972 and XJ24-24A. YCR28 encodes a putative protein of 512 amino acids with some similarities to yeast allontoate permease. Its disruption does not cause any detectable phenotype on rich medium or on allantoate medium, while we observed a strain-dependent effect on sensitivity to amino acid balance and to 3-aminotriazole, when cells were grown in synthetic medium.

Amino Acid Sequence↗

PubMed1990

Nucleotide sequence and characterization of temperature-sensitive pol1 mutants of Saccharomyces cerevisiae.

We have analyzed the effects of temperature-sensitivity (ts)-conferring mutations in the Saccharomyces cerevisiae DNA polymerase I-encoding gene on cell growth, in vivo DNA synthesis, intrachromosomal gene conversion and pop-out recombination. Also, we have identified the molecular defect responsible for the ts phenotype. Two mutant alleles (cdc17-1, cdc17-2) were originally identified as cell-cycle mutations, while a third mutation (hpr3) was found during a genetic screening for mutants with a hyper-recombination phenotype. Both cdc17-2 and hpr3 cells complete one round of cell division and DNA replication after shift to nonpermissive temperature, before being arrested as dumbbell-shaped cells. Conversely, the cdc17-1 mutation immediately blocks growth and DNA synthesis at 37 degrees C. No substantial difference was observed in the frequency of intrachromosomal gene conversion and pop-out recombination events, when hpr3 and cdc17-1 were compared to the previously characterized pol1-1 mutant. These two frequencies were ten- to 30-fold above wild-type level at semipermissive temperature. In each mutant, a single bp substitution, causing the replacement of Gly residues by either Asp (cdc17-1, cdc17-2) or Glu (hpr3) in yeast DNA polymerase I is responsible for the ts phenotype.

Amino Acid Sequence↗

PubMed1988

The yeast DNA polymerase-primase complex: genes and proteins.

The yeast DNA polymerase-primase complex is composed of four polypeptides designated p180, p74, p58 and p48. All the genes coding for these polypeptides have now been cloned. By protein sequence comparison we found that yeast DNA polymerase I (alpha) shares three major regions of homology with several DNA polymerases. A fourth region, called region P, is conserved in yeast and human DNA polymerase alpha. The site of a temperature-sensitive mutation in the POL1 gene which causes decreased stability of the polymerase-primase complex has been sequenced and falls in this region. We hypothesize that region P is important for protein-protein interactions. Highly selective biochemical methods might be similarly important to distinguish functional domains in the polymerase-primase complex. An autocatalytic affinity labeling procedure has been applied to map the active center of yeast DNA primase. From this approach we conclude that both primase subunits (p48 and p58) participate in the formation of the catalytic site of the enzyme.

Amino Acid Sequence↗

PubMedDate not supplied

S-phase DNA damage checkpoint in budding yeast.

Eukaryotic cells must be able to coordinate DNA repair, replication and cell cycle progression in response to DNA damage. A failure to activate the checkpoints which delay the cell cycle in response to internal and external cues and to repair the DNA lesions results in an increase in genetic instability and cancer predisposition. The use of the yeast Saccharomyces cerevisiae has been invaluable in isolating many of the genes required for the DNA damage response, although the molecular mechanisms which couple this regulatory pathway to different DNA transactions are still largely unknown. In analogy with prokaryotes, we propose that DNA strand breaks, caused by genotoxic agents or by replication-related lesions, trigger a replication coupled repair mechanism, dependent upon recombination, which is induced by the checkpoint acting during S-phase.

DNA Damage↗