The type-IV secretion system (T4SS) is a machinery able to transfer DNA and proteins between bacteria and in certain cases also to eukaryotic cells. This thesis compared the T4SSs present in... Show moreThe type-IV secretion system (T4SS) is a machinery able to transfer DNA and proteins between bacteria and in certain cases also to eukaryotic cells. This thesis compared the T4SSs present in Agrobacterium tumefaciens and the conjugative plasmid RP4. A. tumefaciens is able to transfer DNA into plant cells and transform them genetically. We discovered that a novel hairpin structure on the terminus of the transferred DNA allows for earlier expression of its genes in the recipient plant cell. Further, we could describe the translocation signal of the relaxase protein TraI of RP4 responsible for DNA processing and transfer via the T4SS. Additionally, it was shown that the T4SS of RP4 is able to translocate proteins from one cell to another without parallel DNA transfer. Furthermore, we were able to create a hybrid relaxase created consisting of parts from A. tumefaciens (relaxase part) and RP4 (translocation signal) that was shown to be translocated via the T4SS of RP4. Show less
When observing star-forming galaxies, we are not only seeing stellar light, but we also see how this interacts with galactic gas and dust. This thesis contains studies of the stellar, nebular and... Show moreWhen observing star-forming galaxies, we are not only seeing stellar light, but we also see how this interacts with galactic gas and dust. This thesis contains studies of the stellar, nebular and dust properties of low mass star-forming galaxies. We analyse data from the first statistical sample of low mass galaxies with stellar masses down to 10^7 solar masses, and investigate the emission from the stellar populations and their impact on and properties of the ionised surrounding gaseous nebulae, in order to understand the amount of ionising photons that are produced and the fraction of these that can escape from the galaxies. Since the stellar masses in low-mass systems may be stochastically sampled, we predict the influence of this on their nebular emission lies, and in particular on the derivation of their gas metallicity (the abundances of elements heavier than hydrogen and helium in the gas). To interpret observations of galaxies correctly, it is important to know the amount of interstellar dust grains, and its impact on the stellar and nebular light. We therefore finalise this thesis with a new method to derive dust properties in star-forming galaxies. Show less
Stars near massive black holes move on elliptical orbits which precess slowly, exerting persistent gravitational torques on each other. In this the- sis we present four important consequences of... Show moreStars near massive black holes move on elliptical orbits which precess slowly, exerting persistent gravitational torques on each other. In this the- sis we present four important consequences of these gravitational torques: 1) A new instability which exposes the inherently unstable nature of ec- centric stellar disks in galactic nuclei, 2) A density depression of stars near massive black holes due to enhanced angular momentum relaxation and tidal disruptions, 3) A signature of high-eccentricity orbits for stars formed by Hills__ mechanism at large radii from the massive black hole, and a directly-observable statistic that can highlight these populations, and 4) A new dynamical process which we call "secular dynamical anti-friction" which boosts the orbital eccentricity of hypothesized intermediate-mass black holes as they spiral into massive black holes Show less
This thesis describes experiments, in which we used an optical-tweezers setup to study a number of biological systems. We studied the interaction between the E. coli molecular chaperone SecB and a... Show moreThis thesis describes experiments, in which we used an optical-tweezers setup to study a number of biological systems. We studied the interaction between the E. coli molecular chaperone SecB and a protein that was being unfolded and refolded using our optical tweezers setup. Our measurements clearly showed that in the presence of SecB, an unfolded protein could not refold. Molecular dynamics simulations were used to successfully explain features that were observed in our unfolding experiments. Our approach enables studies on other chaperones, as well. Next, we aimed to study translocation of single proteins through membranes by the E. coli Sec translocase. We modified an often-used model protein for our experiment. Different used experimental strategies are presented. Future experiments should enable measurements on the translocation of a single protein. The last study was on the packaging of double-stranded DNA by a single bacteriophage phi29. We aimed to study the effect of multivalent cations on the negatively-charged, tightly-packed DNA inside the bacteriophage capsid and in that way on the speed of the packaging process. A special DNA molecule was constructed and used in a number of successful packaging experiments. Future experiments should show the effect of cations on the packaging rate. With Summary in Dutch Show less
