Structures and roles of the polymorphic forms of tobacco mosaic virus protein: VI. Assembly of the nucleoprotein rods of tobacco mosaic virus from the protein disks and RNA

The assembly of tobacco mosaic virus involves a preformed protein aggregate, the disk, which consists of two rings each of 17 protein subunits, as the sole protein source. The kinetics of this assembly have been studied, using both tobacco mosaic virus RNA, which causes a rapid initiation and so enables growth to be studied, and also polyadenylic acid, with which initiation is slowed down and thus can be partially resolved from growth. Two disks interact with a special nucleotide sequence at the 5′-hydroxyl end of a single tobacco mosaic virus RNA molecule to initiate the formation of the viral nucleoprotein helix, which then grows by the addition of further disks. All of the subunits from these further disks are incorporated into the helix, so that growth proceeds by the co-operative addition of 34 subunits at a time. Under the conditions used, rearrangement of each disk takes about six seconds, giving a total time for the growth of a complete virus particle of just over six minutes.