Prof. Mario Feingold – Dept. of Physics
Single Molecule Studies of DNA-protein interactions - We use Optical Tweezers to manipulated
single DNA molecules. This method can be used to probe various processes in which the DNA
plays a role. In particular, we propose to use this approach to study the interaction between the
DNA and sequence specific proteins. Such protein will first search for the appropriate sequence on
the DNA and once it has found it will initiate a binding process. These processes will influence the
DNA that, in turn, will affect the position of the bead in the optical trap. The displacements that
need to be observed in order to monitor such process are in the nanometer range and are the limit of
the resolution of such a setup. On the other hand, one could amplify the effect by using a DNA that
has several copies of the binding sequence.
Single Cell Dynamics - We use single cell phase-contrast and fluorescence time-lapse microscopy
to monitor the morphological changes during the division of E. coli. To bypass the limitations of
optical resolution, we process the images using pixel intensity values for edge detection. We study
the dynamics of the constriction width, W, and find that its formation starts shortly after birth much
earlier than can be detected by simply viewing phase-contrast images. A simple geometrical model
is shown to reproduce the behavior of W(t). Moreover, the time-dependence of the cell length, L(t),
consists of three linear regimes. The growth rates in the different regimes are related to each other
and to the parameters of our model.
Phase-contrast (right) and fluorescence (left) images of E.coli bacteria, stained with FM
4-64.
Tree elongation regimes in a single bacterium.