Plant viruses were the first biological objects to be reconstituted in vitro. This may be considered an eloquent proof of our correct understanding of a set of components comprising the reconstituted object. The possibility of reconstitution in vitro has been demonstrated for a whole number of biological objects besides viruses, such as bacterial ribosome subunits, membrane vesicules, etc. It was demonstrated that barley stripe mosaic virus (BSMV) protein subunits can assemble in vitro into structures resembling those of an intact virus. The process of BSMV protein polymerization proceeds step-wise through a number of stable intermediates of increasing size. A characteristic feature of the filamentous viruses is a slightly curved appearance of their particles detected by electron microscopy. Capsid protein subunits initiate TMV assembly from an internal site near the 3'-terminal of its RNA followed by bidirectional encapsidation of the RNA.