On the inside of the protein capsid is a single-stranded RNA molecule coiled into a helix. The strand is spirally wound and fol1ows the pitch of the protein helix. Each turn of the RNA helix contains 49 nucleotides and has a pitch of 23°C. There are 49 protein subunits associated with three turns of the RNA helix, i. e. 16⅓ protein subunits per turn of the helix.
Thus each, protein subunit is, associated with three nucleotide residues of RNA. The molecular weight of TMV RNA is 2.06 x 106 daltons. The RNA is infective by itself, although much less so than the intact virion. This is because unprotected RNA is subjected to the action of enzymes (nucleases) and is degraded. The protein functions as a protective tube around the RNA. In vivo, TMV RNA directs the, synthesis of several proteins: coat protein (MW 17,500 daltons) and two large polypeptides (MW 160)000 and 140,000).
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