Glycine betaine, which functions as an osmoprotectant, is accumulated to high intracellular concentrations in Escherichia coli at high osmolarity. We demonstrate the presence of a high-affinity, binding protein dependent transport system for glycine betaine, which is encoded by the proU region. We show the osmotically regulated synthesis of a 32 kDa periplasmic protein that is a glycine betaine binding protein with a KD of 1.4 microM. ProU-mediated glycine betaine transport is osmotically stimulated at the level of gene expression. The osmolarity of the medium also regulates the activity of the transport system, while binding of glycine betaine to its binding protein is independent of the osmolarity. We also find a second glycine betaine transport system that is dependent on proP and exhibits a lower substrate affinity. Like ProU, this system is regulated at two levels: both gene expression and the activity of the transport system are osmotically stimulated. Using lambda plac Mu-generated lacZ operon and gene fusions, we find that expression of the proU region is osmotically regulated at the level of transcription. We cloned a part of the proU region together with the phi(proU-lacZ)hyb2 gene fusion into a multicopy plasmid and show that the DNA sequences required in cis for osmotic regulation are present on the plasmid.
To explore the reasons for the dearth of minorities in Ph.D.-level biomedical research and identify opportunities to increase minority participation, we surveyed high-achieving alumni of an undergraduate biology enrichment program for underrepresented minorities. Respondents were asked to describe their career paths and to reflect on the influences that guided their career choices. We particularly probed for attitudes and experiences that influenced students to pursue a research career, as well as factors relevant to their choice between medicine (the dominant career choice) and basic science. In agreement with earlier studies, alumni strongly endorsed supplemental instruction as a mechanism for achieving excellence in basic science courses. Undergraduate research was seen as broadening by many and was transformative for half of the alumni who ultimately decided to pursue Ph.D.s in biomedical research. That group had expressed no interest in research careers at college entry and credits their undergraduate research experience with putting them on track toward a research career. A policy implication of these results is that making undergraduate research opportunities widely available to biology students (including "premed" students) in the context of a structured educational enrichment program should increase the number of minority students who choose to pursue biomedical Ph.D.s.
A comprehensive, quantitative evaluation of an educational intervention program designed to reduce the attrition of minorities from the biological sciences was undertaken to ascertain whether such efforts adequately address the problem. Program participants had greater odds of persisting in basic math and science courses, and of graduating in biology, than did a comparison group, controlling for demographics and academic preparation. Undergraduate research greatly increased the odds of positive graduation outcomes. Program participants were also more likely to pursue graduate study than were university graduates overall. This evaluation demonstrates the value of such programs in increasing the representation of minorities in science. ß
A new osmotically inducible gene in Escherichia coli, osmY, was induced 8- to 10-fold by hyperosmotic stress and 2- to 3-fold by growth in complex medium. The osmY gene product is a periplasmic protein which migrates with an apparent molecular mass of 22 kDa on sodium dodecyl sulfate-polyacrylamide gels. A genetic fusion to osmY was mapped to 99.3 min on the E. coli chromosome. The gene was cloned and sequenced, and an open reading frame was identified. The open reading frame encoded a precursor protein with a calculated molecular weight of 21,090 and a mature protein of 18,150 following signal peptide cleavage. Sequencing of the periplasmic OsmY protein confirmed the open reading frame and defined the signal peptide cleavage site as Ala-Glu. A mutation caused by the osmY::TnphoA genetic fusion resulted in slightly increased sensitivity to hyperosmotic stress.
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