Electron microscopy, distances proteins

Fig. 30. The 19 protein neutron map of the 30S ribosomal subunit determined by label triangulation (right). The proteins are depicted as spheres whose volumes are to scale. For clarity, several spheres are drawn unfilled. The centre-to-centre distance between S13 and S17 is 17.3 nm [490]. The left view shows the electron microscopy model of the 30S subunit and the sites of the antigenic determinants from immune electron microscopy techniques [490]. Note that most of the protein is located to the top of the model as viewed, while the RNA is predominant in the lower half.

We do not know wheflier in the case of active complexes die enzyme is interacting directly with the strand break or if die loop formation allows die poly(ADP-ribose) polymerase to act at a distance. This last hypothesis would require either the presence of two DNA binding sites on the same molecule or die possibility for the enzyme to form dimers as in the case of gyrase-DNA complexes (13) or for proteins involved in gene regulation where DNA bending and loop formation was observed by electron microscopy (15,16). 

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