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In this study, the homodimeric and heteromeric nature of ProP, an H+/solute symporter, from E. coli was analyzed. The measured initial rates of proline uptake via ProP-His6 and His6-ProP indicated that as the growth medium osmolality increased, the assay medium osmolality required for half maximal transport activity (Π½/RT) increased and the maximal uptake rate (Amax) decreased. The oligomeric state of ProP, as determined by Blue Native PAGE, showed that both monomeric and dimeric forms of the transporter were present in wild type and cardiolipin deficient bacteria expressing ProP, ProP-His6 or His6-ProP, after culturing in low or high growth medium osmolality. The BACTH System was used to confirm the homodimeric ProP-ProP interaction and to verify the heteromeric interaction between ProP and YdhP. Initial rates of proline uptake via ProP and Western blots indicated that replacement of the ydhP locus with a kanamycin cassette had no effect on ProP function or expression.

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The discovery of penicillin ushered in the era of the mass use of antibiotics in clinical settings. Today the development of antibiotic resistance and lack of discoveries of new antibiotics have created a serious public health concern. Recently, new experimental tools, such as bacterial genome-wide deletion collections, have provided exciting new possibilities for studying biological networks in bacteria that could potentially also be exploited for antibiotic research. In this study, I used the Keio knockout collection of Escherichia coli (E.coli) strains, along with an in-house collection of hypomorphic alleles of essential genes, to study the effects of chemical perturbations by twenty-two antibiotics and four other chemicals on the biological pathways of E.coli. These experiments uncovered a set of mutants hypersensitive to drugs of different classes, information which could potentially be exploited for future antibiotic research. The results also shed light on how different classes of antibiotics behave with respect to their target pathways and the various functional modules with which they are associated.