The Significance of the Nuclear Gene, SGS1, in Mitochondrial Genome Stability in Saccharomyces cerevisiae

The homologs that humans share with Saccharomyces cerevisiae render yeast an ideal model organism to investigate the potential importance of genes in humans. SGS1 is a nuclear gene for a RecQ helicase in yeast, known to play a role in homologous recombination in nuclear genome repair. The research in question is intended to evaluate if SGS1 has a similar importance in mitochondrial genome repair. These conclusions can be employed to better understand the disease phenotypes that humans present as a result from mitochondrial malfunction. A respiration loss assay showed that SGS1 knockout strains have a ~2.2 fold increase in spontaneous respiration loss frequency, indicating that SGS1 plays a role in mitochondrial genome stability. A direct-repeat mediated deletion assay proves SGS1 is involved in homologous recombination in mitochondria due to an ~1.6 fold decrease in rate of homologous recombination in SGS1 knockout strains. With a p value of 0.66, no significant difference was observed in an induced direct-repeat mediated deletion assay between wild type and sgs1Δ strains, implying that SGS1 does not play a fundamental role in double strand break repair. Future experimentation could include additional knockout strains testing other genes known to be involved in nuclear homologous recombination repair and double knockout strains to assess the relative order of active proteins involved in genetic repair mechanisms

The Significance of the Nuclear Gene, SGS1, in Mitochondrial Genome Stability in Saccharomyces Cerevisiae

Mitochondria are essential organelles in eukaryotes. Mitochondria synthesize ATP, supplying the cell with energy necessary for metabolic processes, hence its nickname of the cell’s “powerhouse”. Mitochondria have individual genomes, separate from the nuclear DNA, that encode proteins vital for respiration. In humans, mutations in the mitochondrial DNA (mtDNA) lead to several neuromuscular and neurodegenerative disorders due to the compromised stability of mtDNA. This particular study focuses on a nuclear gene, SGS1, and its significance in mtDNA stability in the budding yeast, Saccharomyces cerevisiae. SGS1 is a member of the recQ family of helicases and therefore aids in the unwinding of chromatin at the duplex as it prepares for replication.[1] Similar mutations in homologs of SGS1 helicase lead to specifically, Bloom Werner and Rothmund-Thomson syndromes in humans.[1] Yeast lacking functional Sgs1p protein display hypersensitivity to DNA-damaging agents and hyper-recombination and exhibit signs of premature aging.[1] The quantitative impacts of SGS1 mutations on mtDNA stability in budding yeast was studied via genetic assays that measured spontaneous respiration loss and direct repeat mediated deletion. Budding yeast sgs1∆ display an ~2.2fold increase in respiration loss. From two independent isolates, sgs1∆ mutants have also shown an ~1.7 and ~1.5 decrease in mitochondrial homologous recombination, but ~2.4 and ~2.8 increase in nuclear homologous recombination. The nuclear data supports existing conclusions. Our data shows that the presence of Sgs1p protein plays a role in mitochondrial genome stability

INFLUENCE OF AGE, SEX, AND BODY HABITUS ON THE MEAN QRS ELECTRICAL AXIS IN CHILDHOOD AND ADOLESCENCE

The "mean QRS electrical axis " has been defined by Ziegler (1951) as the average direction in which the excitatory process spreads throughout the ventricular myocardium. This mean axis or vector in the frontal plane may be calculated from the standard limb leads and used as an index of cardiac abnormality. In biometrics the term "deviation " is usually used to indicate the departure of a measurement from an established normal value. Thus in electrocardiography right or left axis deviation denotes departure of the electrical forces from the normal toward one or other side of the body. Accurate interpretation of such deviation is dependent upon well-established normal standards, and several authorities (Johnston, 1961; Ezra, 1961; Milnor, 1962) have indicated that those values currently available for older children and adolescents are inadequate. Most previous studies have contained insufficient numbers to permit statistical analysis (Lincoln and Nicolson