What's in a Prerequisite? A Mixed-Methods Approach to Identifying the Impact of a Prerequisite Course.

Despite the ubiquity of prerequisites in undergraduate science, technology, engineering, and mathematics curricula, there has been minimal effort to assess their value in a data-driven manner. Using both quantitative and qualitative data, we examined the impact of prerequisites in the context of a microbiology lecture and lab course pairing. Through interviews and an online survey, students highlighted a number of positive attributes of prerequisites, including their role in knowledge acquisition, along with negative impacts, such as perhaps needlessly increasing time to degree and adding to the cost of education. We also identified a number of reasons why individuals do or do not enroll in prerequisite courses, many of which were not related to student learning. In our particular curriculum, students did not believe the microbiology lecture course impacted success in the lab, which agrees with our analysis of lab course performance using a previously established "familiarity" scale. These conclusions highlight the importance of soliciting and analyzing student feedback, and triangulating these data with quantitative performance metrics to assess the state of science, technology, engineering, and mathematics curricula.

Protein kinase A regulates resumption of meiosis by phosphorylation of Cdc25B in mammalian oocytes.

In mammalian oocytes, meiosis arrests at prophase I. Meiotic resumption requires activation of Maturation-Promoting Factor (MPF), comprised of a catalytic Cyclin-dependent kinase-1 (Cdk1) and a regulatory subunit cyclin B and results in germinal vesicle breakdown (GVBD). Cyclic AMP (cAMP)-mediated Protein Kinase A (PKA) activity sustains prophase arrest by inhibiting Cdk1. However, the link between PKA activity and MPF inhibition remains unclear. Cdc25 phosphatases can activate Cdks by removing inhibitory phosphates from Cdks. Thus one method for sustaining prophase arrest could be inhibition of the activity of the Cdc25 protein required for MPF activation. Indeed, studies in Xenopus identify Cdc25C as a target of PKA activity in meiosis. However, in mice, studies suggest that Cdc25B is the phosphatase essential for GVBD and, therefore, the likely target of PKA activity. To assess these questions, we targeted a potential PKA substrate, a highly conserved serine 321 residue of Cdc25B and evaluated the effect on oocyte maturation. A Cdc25B-Ser321Ala point mutant mRNA induces GVBD when injected into prophase-arrested oocytes more rapidly than wild type mRNA. Using fluorescently-tagged proteins we also determined that the mutant protein enters the nucleus more rapidly than its wildtype counterpart. These data suggest that phosphorylation of the Ser321 residue plays a key role in the negative regulation and localization of Cdc25B during prophase arrest. PKA also phosphorylates a wildtype Cdc25B protein but not a Ser321Ala mutant protein in vitro. Mutation of Ser321 in Cdc25B also affects its association with a sequestering protein, 14-3-3. Our studies suggest that Cdc25B is a direct target of PKA in prophase-arrested oocytes and that Cdc25B phosphorylation results in its inhibition and sequestration by the 14-3-3 protein.

Structure of the Bateman2 domain of yeast Snf4: dimeric association and relevance for AMP binding.

AMP-activated protein kinase (AMPK) is a central regulator of energy homeostasis in mammals. AMP is believed to control the activity of AMPK by binding to the gamma subunit of this heterotrimeric enzyme. This subunit contains two Bateman domains, each of which is composed of a tandem pair of cystathionine beta-synthase (CBS) motifs. No structural information is currently available on this subunit, and the molecular basis for its interactions with AMP is not well understood. We report here the crystal structure at 1.9 Angstrom resolution of the Bateman2 domain of Snf4, the gamma subunit of the yeast ortholog of AMPK. The structure revealed a dimer of the Bateman2 domain, and this dimerization is supported by our light-scattering, mutagenesis, and biochemical studies. There is a prominent pocket at the center of this dimer, and most of the disease-causing mutations are located in or near this pocket.

Peculiarities of flor strains adapted to Sardinian sherry-like wine ageing conditions.

Saccharomyces cerevisiae flor yeasts, which are subjected to stressful conditions during wine ageing, exhibit a number of characteristics which distinguish them from non-flor S. cerevisiae wine strains. In the present work, 22 flor and 14 non-flor S. cerevisiae wine strains are compared, in order to elucidate other possible peculiarities of these yeasts. The results obtained demonstrate that in contrast to the homothallic nature of the non-flor strains, 77% of the flor strains exhibit two variants of a semi-homothallic life cycle. Moreover, the flor-forming ability is shown to be inversely correlated to spore viability and the utilisation of maltose and galactose.

FLO11-based model for air-liquid interfacial biofilm formation by Saccharomyces cerevisiae.

Sardinian wine strains of Saccharomyces cerevisiae used to make sherry-like wines form a biofilm at the air-liquid interface at the end of ethanolic fermentation, when grape sugar is depleted and further growth becomes dependent on access to oxygen. Here, we show that FLO11, which encodes a hydrophobic cell wall glycoprotein, is required for the air-liquid interfacial biofilm and that biofilm cells have a buoyant density greater than the suspending medium. We propose a model for biofilm formation based on an increase in cell surface hydrophobicity occurring at the diauxic shift. This increase leads to formation of multicellular aggregates that effectively entrap carbon dioxide, providing buoyancy. A visible biofilm appears when a sufficient number of hydrophobic cell aggregates are carried to and grow on the liquid surface.

Diversity of Y region at HML locus in a Saccharomyces cerevisiae strain isolated from a Sardinian wine.

Several mutations in genes involved in Saccharomyces mating type switching may affect the homothallic behaviour in wine yeasts. In this study the semi-homothallic (Hq) segregation of a flor wine yeast strain was analysed. We aimed to understand the molecular basis of this behaviour in a flor autochthonous strain, verifying the MAT locus status by a PCR-based HO gene disruption and sequencing of the Y region of the HML, HMR and MAT loci, after nested PCR. Presence of ORFs a1 and a2 in the Y region of the HML locus was found. At the ORF a2 at HML locus, a mutation in the stop codon was found, so the a2 ORF contains 33 more bases.