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Different models have been proposed for the nature of the potexvirus transport form that moves from cell to cell over the infected plant: (i) genomic RNA moves as native virions; or (ii) in vitro-assembled non-virion ribonucleoprotein (RNP) complexes consisting of viral RNA, coat protein (CP) and movement protein (MP), termed TGBp1, serve as the transport form in vivo. As the structure of these RNPs has not been elucidated, the products assembled in vitro from potato virus X (PVX) RNA, CP and TGBp1 were characterized. The complexes appeared as single-tailed particles (STPs) with a helical, head-like structure composed of CP subunits located at the 59-proximal region of PVX RNA; the TGBp1 was bound to the terminal CP molecules of the head. Remarkably, no particular non-virion RNP complexes were observed. These data suggest that the CP-RNA interactions resulting in head formation prevailed over TGBp1-RNA binding upon STP assembly from RNA, CP and TGBp1. STPs could be assembled from the 59 end of PVX RNA and CP in the absence of TGBp1. The translational ability of STPs was characterized in a cell-free translation system. STPs lacking TGBp1 were entirely non-translatable; however, they were rendered translatable by binding of TGBp1 to the end of the head. It is suggested that the RNA-mediated assembly of STPs proceeds via two steps. Firstly, non-translatable CP-RNA STPs are produced, due to encapsidation of the 59-terminal region. Secondly, the TGBp1 molecules bind to the end of a polar head, resulting in conversion of the STPs into a translatable form.

This paper is dedicated to atomic force microscopy (AFM) as a progressive tool for imaging bacterial surfaces and probing their properties. The description of the technique is complemented by the explanation of the method's artifacts typical, in particular, for the imaging of bacterial cells. Sample preparation techniques are summarized in a separate section. Special attention is paid to the differences in imaging of gram-positive and gram-negative bacteria. Probing of mechanical properties, including elastic modulus, fragility, and adhesion of the cell walls is emphasized. The advantages of AFM in the studies of real-time cellular dynamical processes are illustrated by the experiment with the germination of spores.

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