[Model for tobacco mosaic virus assembly in vitro: specific dislocation by cooperative single-letter purine recognition and non-cooperative RNA "locking" between subunit layers].

A model of the molecular mechanism of tobacco mosaic virus (TMV) assembly in vitro is proposed. The model is based on the assumption that on interaction of TMV RNA chain with a double protein disk two different types of structural alterations occur in the protein subunits: "dislocating alterations" leading to screw dislocation of the disk into a helix fragment and "locking alterations" leading to locking of the RNA chain between the subunits layers. During initiation of TMV assembly the dislocating alterations occur cooperatively in all subunits of the disk as a result of specific interaction of purines (guanines) in the middle (horizontal) position of every trinucleotide unit with the 32--39 loop of the TMV protein molecule. Locking alterations are induced non-cooperatively by phosphate groups and lateral (vertical) bases of trinucleotide units. The sequence of events during TMV assembly in vitro and the role of topological factors in this process are discussed.